[usth/ICT2.1] Algorithm and Data Structures

43 files changed, 1658 insertions, 1 deletions

diff --git a/README.md b/README.md
index 5408e6f..a06bc18 100644
--- a/README.md
+++ b/README.md
@@ -2,7 +2,7 @@
 
 This used to be my competitive programming collection, now it is more of
 a warehouse for my computer programming journey.  For historical reasons,
-this README as well as commit messages are duolingo (Anglais et Vietnamien).
+this README as well as commit messages are duolingo (anglais et vietnamien).
 
 |    Thư mục   |                      Nguồn đề bài                      |
 | ------------ | ------------------------------------------------------ |
@@ -39,6 +39,7 @@ Phiên bản các trình dịch sử dụng test:
 | Common Lisp | SBCL 1.4.8+        |
 | Java        | OpenJDK 11+        |
 | Lua         | Lua 5.1+           |
+| Octave      | Octave 6+          |
 | Pascal      | Free Pascal 2.6.4+ |
 | Python      | Python 3.5+        |
 | Raku        | Rakudo 2018.12+    |
diff --git a/usth/ICT2.1/final/problem1.c b/usth/ICT2.1/final/problem1.c
new file mode 100644
index 0000000..dce5ca7
--- /dev/null
+++ b/usth/ICT2.1/final/problem1.c
@@ -0,0 +1,33 @@
+/* Read a natural number from stdin and print its divisors to stdout */
+#include <stdio.h>
+
+/* Print all divisors of the given natural number n. */
+void print_divisors(int n, int i)
+{
+	if (i * i == n)
+		printf("%d\n", i);		/* Θ(1) */
+	if (i * i >= n)
+		return;				/* Θ(1) */
+	if (n % i == 0)
+		printf("%d\n%d\n", i, n / i);	/* Θ(1) */
+	print_divisors(n, i + 1);
+}
+
+/*
+ * Complexity analysis:
+ * Let T(n, i) be the time complexity of print_divisors, it is obvious that
+ *     T(n, i) = Θ(1) if i*i >= n
+ *     T(n, i) = T(n, i + 1) + Θ(1)
+ * Thus T(n, 1) = sum(Θ(1) for i from 1 to ceil(sqrt(n))) = Θ(sqrt(n))
+ * or the overall time complexity of the call from main is Θ(sqrt(n))
+ * on all scenarios.
+ */
+int main()
+{
+	int n;
+
+	scanf("%d", &n);
+	print_divisors(n, 1);
+
+	return 0;
+}
diff --git a/usth/ICT2.1/final/problem2.c b/usth/ICT2.1/final/problem2.c
new file mode 100644
index 0000000..1b3368d
--- /dev/null
+++ b/usth/ICT2.1/final/problem2.c
@@ -0,0 +1,127 @@
+/*
+ * Read one natural number from stdin and print its prime factors to stdout
+ * The time complexity analysis of this program is commented in the source code
+ */
+#include <stdio.h>
+#include <stdlib.h>
+
+typedef struct list construct;
+struct list {
+	void *car;
+        construct *cdr;
+};
+
+typedef struct {
+	construct *stack;
+} stack;
+
+construct *cons(void *first, construct *rest)
+{
+	construct *list = malloc(sizeof(construct));
+	list->car = first;
+	list->cdr = rest;
+	return list;
+}
+
+void *car(construct *list)
+{
+	return list->car;
+}
+
+construct *cdr(construct *list)
+{
+	return list->cdr;
+}
+
+stack *mkstack()
+{
+	stack *s = malloc(sizeof(stack));
+	s->stack = NULL;
+	return s;
+}
+
+int stack_empty(stack *s)
+{
+	return s->stack == NULL;
+}
+
+void stack_push(stack *s, void *item)
+{
+	s->stack = cons(item, s->stack);
+}
+
+void *stack_top(stack *s)
+{
+	return car(s->stack);
+}
+
+void *stack_pop(stack *s)
+{
+	void *first = car(s->stack);
+	construct *rest = cdr(s->stack);
+	free(s->stack);
+	s->stack = rest;
+	return first;
+}
+
+int main()
+{
+	int n, m;		/* Θ(1) */
+	stack *s = mkstack();	/* Θ(1) */
+
+	scanf("%d", &n);	/* Θ(1) */
+	m = n;			/* Θ(1) */
+	/*
+	 * Let P be the sequence of prime factors of n and l be length of P.
+	 * Let T(n, 2) be the time complexity of this for loop.
+	 * Consider the function T(n, i):
+	 *     T(n, i) = Θ(1) if i*i >= n
+	 *     T(n, i) = T(n, i + 1) + Θ(1) if n is not divisible by i	(*)
+	 *     T(n, i) = T(n/i, i) + Θ(1) if n is divisible by i	(**)
+	 *
+	 * If only the (*) recurrence occurs, it is the worst case and
+	 *     T(n, 2) = sum(Θ(1) for i from 2 to floor(sqrt(n))) = Θ(sqrt(n))
+	 *
+	 * If only the (**) recurrence occurs, it is the best case where n
+	 * is power of 2.  For convenience, we define R(n) = T(n, 2) and get
+	 *     R(n) = 1R(n/2) + Θ(n^log2(1))
+	 * By the master theorem,
+	 *     R(n) = Θ(n^log2(1) lg(n)) = Θ(lg(n)).
+	 *
+	 * If both occurs (average case), I can imagine that there exist numbers
+	 * n_0, n_1, etc. and m_0, m_1, etc. that
+	 *     T(n, 2) = sum(Θ(sqrt(n_i))) + sum(Θ(lg(m_i))) = Θ(sqrt(n))
+	 * I, however, fail to formulate a rigorous proof for this.
+	 */
+	for (int i = 2; i * i <= n; ++i)
+		while (n % i == 0) {
+			int *tmp = malloc(sizeof(int)); /* Θ(1) */
+			*tmp = i;			/* Θ(1) */
+			stack_push(s, tmp);		/* Θ(1) */
+			n /= i;				/* Θ(1) */
+		}
+	if (n != 1) {
+		int *tmp = malloc(sizeof(int));
+		*tmp = n;
+		stack_push(s, tmp);
+	}	/* Θ(1) */
+
+	/*
+	 * Since each iteration of the loop above produce at most one
+	 * prime factor, the time complexity of the loop below is O(T(n, 2)).
+	 */
+	while (!stack_empty(s)) {
+		printf("%d * ", *(int *) stack_top(s));		/* Θ(1) */
+		stack_pop(s);					/* Θ(1) */
+	}
+	/* Terrible hack, not even portable (depending on flush behavior) */
+	printf("\b\b= %d\n", m);				/* Θ(1) */
+
+	return 0;
+}
+
+/*
+ * Conclusion on time complexity:
+ * Best case:  Θ(lg(n)) + O(Θ(lg(n))) = Θ(lg(n))
+ * Average case and worst case:  Θ(sqrt(n)) + O(Θ(sqrt(n))) = Θ(sqrt(n))
+ */
diff --git a/usth/ICT2.1/labwork/1/Bonus.c b/usth/ICT2.1/labwork/1/Bonus.c
new file mode 100644
index 0000000..e98bee5
--- /dev/null
+++ b/usth/ICT2.1/labwork/1/Bonus.c
@@ -0,0 +1,25 @@
+/*
+ * Read an integer from stdin and print its prime factors to stdout
+ * This is free and unencumbered software released into the public domain.
+ */
+
+#include <stdio.h>
+
+int main()
+{
+	unsigned n, m = 0;
+
+	scanf("%u", &n);
+
+	for (unsigned i = 2; i * i <= n; ++i)
+		while (n % i == 0) {
+			printf(m++ ? " %u" : "%u", i);
+			n /= i;
+		}
+	if (n != 1)
+		printf(m++ ? " %u" : "%u", n);
+	if (m)
+		putchar(10);
+
+	return 0;
+}
diff --git a/usth/ICT2.1/labwork/1/Ex1.cc b/usth/ICT2.1/labwork/1/Ex1.cc
new file mode 100644
index 0000000..da20f22
--- /dev/null
+++ b/usth/ICT2.1/labwork/1/Ex1.cc
@@ -0,0 +1,28 @@
+// Read two integers from stdin and print their sum and product
+// This is free and unencumbered software released into the public domain.
+
+#include <iostream>
+
+using namespace std;
+
+int
+add (int& a, int& b)
+{
+  return a + b;
+}
+
+int
+mul (int& a, int& b)
+{
+  return a * b;
+}
+
+int
+main ()
+{
+  int a;
+  int b;
+
+  cin >> a >> b;
+  cout << add (a, b) << endl << mul (a, b) << endl;
+}
diff --git a/usth/ICT2.1/labwork/1/Ex2.c b/usth/ICT2.1/labwork/1/Ex2.c
new file mode 100644
index 0000000..f783946
--- /dev/null
+++ b/usth/ICT2.1/labwork/1/Ex2.c
@@ -0,0 +1,28 @@
+/*
+ * Read an array of n int from stdin and print its sum to stdout
+ * This is free and unencumbered software released into the public domain.
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+
+int sum(int n, int *a)
+{
+	int s = 0;
+	while (n--)
+		s += a[n];
+	return s;
+}
+
+int main()
+{
+	int n;
+	scanf("%d", &n);
+
+	int *a = malloc(n * sizeof(int));
+	for (int i = 0; i < n; ++i)
+		scanf("%d", a + i);
+
+	printf("%d\n", sum(n, a));
+	return 0;
+}
diff --git a/usth/ICT2.1/labwork/1/Ex3.c b/usth/ICT2.1/labwork/1/Ex3.c
new file mode 100644
index 0000000..f20bb54
--- /dev/null
+++ b/usth/ICT2.1/labwork/1/Ex3.c
@@ -0,0 +1,33 @@
+/*
+ * Read coordinates of 2 2D-points from stdin and print their distance to stdout
+ * This is free and unencumbered software released into the public domain.
+ */
+
+#include <math.h>
+#include <stdio.h>
+
+/*
+ * The overhead caused by re-evaluating x in this case is much
+ * to change this into a function call.
+ */
+#define SQR(x) ((x) * (x))
+
+/* Conventionally C names are in lowercase */
+struct point {
+	double x, y;
+};
+
+double distance(struct point u, struct point v)
+{
+	return sqrt(SQR(u.x - v.x) + SQR(u.y - v.y));
+}
+
+int main()
+{
+	struct point m, n;
+
+	scanf("%lf %lf %lf %lf", &m.x, &m.y, &n.x, &n.y);
+	printf("%g\n", distance(m, n));
+
+	return 0;
+}
diff --git a/usth/ICT2.1/labwork/1/Ex4.c b/usth/ICT2.1/labwork/1/Ex4.c
new file mode 100644
index 0000000..000f73a
--- /dev/null
+++ b/usth/ICT2.1/labwork/1/Ex4.c
@@ -0,0 +1,46 @@
+/*
+ * Print the area of the rectangle constructed from a pair of 2D points
+ * and check if a point it within this rectangle
+ * This is free and unencumbered software released into the public domain.
+ */
+
+#include <math.h>
+#include <stdio.h>
+
+/* Writing a header for just a simple struct would be overkill. */
+struct point {
+	double x, y;
+};
+
+struct rect {
+	struct point u, v;
+};
+
+double area(struct rect r)
+{
+	return fabs((r.u.x - r.v.x) * (r.u.y - r.v.y));
+}
+
+int isin(struct point p, struct rect r)
+{
+	return ((p.x - r.u.x) * (p.x - r.v.x) < 0
+	        && (p.y - r.u.y) * (p.y - r.v.y) < 0);
+}
+
+int main()
+{
+	struct point m, n;
+	/* Don't bother logging errors, since it would pollute the pipe. */
+	do {
+		scanf("%lf %lf %lf %lf", &m.x, &m.y, &n.x, &n.y);
+	} while (m.x == n.x || m.y == n.y);
+
+	struct rect r = {m, n};
+	printf("%g\n", area(r));
+
+	struct point p;
+	scanf("%lf %lf", &p.x, &p.y);
+	printf("%d\n", isin(p, r));
+
+	return 0;
+}
diff --git a/usth/ICT2.1/labwork/1/README.md b/usth/ICT2.1/labwork/1/README.md
new file mode 100644
index 0000000..2d8236b
--- /dev/null
+++ b/usth/ICT2.1/labwork/1/README.md
@@ -0,0 +1,38 @@
+# Algorithms and Data Structures: Tutorial 1
+
+This package contains the following files:
+
+* Ex1.cc
+* Ex2.c
+* Ex3.c
+* Ex4.c
+* Bonus.c
+
+These programs operate on standard I/O directly.  Except for the solution
+of the first exercise which is written in C++, all solutions are in C.
+The source files are as licensed under the Unlicense which states
+
+> This is free and unencumbered software released into the public domain.
+>
+> Anyone is free to copy, modify, publish, use, compile, sell, or
+> distribute this software, either in source code form or as a compiled
+> binary, for any purpose, commercial or non-commercial, and by any
+> means.
+>
+> In jurisdictions that recognize copyright laws, the author or authors
+> of this software dedicate any and all copyright interest in the
+> software to the public domain. We make this dedication for the benefit
+> of the public at large and to the detriment of our heirs and
+> successors. We intend this dedication to be an overt act of
+> relinquishment in perpetuity of all present and future rights to this
+> software under copyright law.
+>
+> THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+> EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+> MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
+> IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR
+> OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
+> ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
+> OTHER DEALINGS IN THE SOFTWARE.
+>
+> For more information, please refer to <http://unlicense.org/>
diff --git a/usth/ICT2.1/labwork/1/TT1.pdf b/usth/ICT2.1/labwork/1/TT1.pdf
new file mode 100644
index 0000000..3140b19
--- /dev/null
+++ b/usth/ICT2.1/labwork/1/TT1.pdf
Binary files differdiff --git a/usth/ICT2.1/labwork/2/Ex1.c b/usth/ICT2.1/labwork/2/Ex1.c
new file mode 100644
index 0000000..b4d5836
--- /dev/null
+++ b/usth/ICT2.1/labwork/2/Ex1.c
@@ -0,0 +1,100 @@
+/*
+ * Train represented using linked list by lisp-like constructs.
+ * This is free and unencumbered software released into the public domain.
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <time.h>
+
+#include "construct.h"
+
+#define N 7
+#define LEN_MAX 42
+#define PSNGR_MAX 5	/* this raises the chance of empty vehicle */
+
+struct vehicle {
+	int passengers;
+	char *name;
+};
+
+void free_vehicle(struct vehicle *v)
+{
+	free(v->name);
+	free(v);
+}
+
+struct vehicle *mkvehicle(int passengers, char *name)
+{
+	struct vehicle *v = malloc(sizeof(struct vehicle));
+	v->passengers = passengers;
+	v->name = name;
+	return v;
+}
+
+struct vehicle *rand_vehicle()
+{
+	int len = rand() % LEN_MAX + 2;	/* avoid empty name */
+	char *name = malloc(len--);
+	for (int j = 0; j < len; ++j)
+		name[j] = 'a' + rand() % 26;
+	name[len] = 0;
+	return mkvehicle(rand() % PSNGR_MAX, name);
+}
+
+void print_vehicle(struct vehicle *v)
+{
+	printf("%s (%d passengers)\n", v->name, v->passengers);
+}
+
+void print_train(construct *train)
+{
+	if (train == NULL)
+		return;
+	print_vehicle(car(train));
+	print_train(cdr(train));
+}
+
+/* Remove empty vehicles */
+construct *optimize_train(construct *train)
+{
+	if (train == NULL)
+		return NULL;
+	struct vehicle *first = car(train);
+	construct *rest = cdr(train);
+	free(train);
+
+	if (first->passengers)
+		return cons(first, optimize_train(rest));
+	free_vehicle(first);
+	return optimize_train(rest);
+}
+
+int main()
+{
+	construct *train = NULL;
+
+	srand(time(NULL));
+	for (int i = 0; i < N; ++i)
+		train = cons(rand_vehicle(), train);
+	puts("Initial train:");
+	print_train(train);
+	putchar(10);
+
+	train = optimize_train(train);
+	puts("Optimized train:");
+	print_train(train);
+	putchar(10);
+
+	int index = rand() % length(train);
+	struct vehicle *v = rand_vehicle();
+	while (!v->passengers) {
+		free(v);
+		v = rand_vehicle();
+	}
+	train = insert(v, train, index);
+	printf("Train after inserting a new one at index %d:\n", index);
+	print_train(train);
+
+	return 0;
+}
diff --git a/usth/ICT2.1/labwork/2/Ex2.c b/usth/ICT2.1/labwork/2/Ex2.c
new file mode 100644
index 0000000..8f32134
--- /dev/null
+++ b/usth/ICT2.1/labwork/2/Ex2.c
@@ -0,0 +1,104 @@
+/*
+ * Polynomial represented using linked list, with free coefficient at last.
+ * This is free and unencumbered software released into the public domain.
+ */
+
+#include <math.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <time.h>
+
+#include "construct.h"
+
+#define COEFF_MOD 42
+
+/*
+ * Add addition to the coefficient of power n of poly if it already exists.
+ * Return the mutated polynomial on success and NULL otherwise.
+ */
+construct *add_term(construct *poly, double addition, size_t n)
+{
+	double *term = nth(poly, length(poly) - n - 1);
+	if (term == NULL)
+		return NULL;
+	*term += addition;
+	return poly;
+}
+
+/* Remove the nth term and return the mutated polynomial. */
+construct *remove_term(construct *poly, size_t n)
+{
+	if (poly == NULL)
+		return NULL;
+	size_t len = length(poly);
+	if (++n == len) {
+		construct *rest = cdr(poly);
+		free(car(poly));
+		free(poly);
+		return rest;
+	}
+
+	double *term = nth(poly, len - n);
+	if (term == NULL)
+		return poly;
+	*term = 0;
+	return poly;
+}
+
+/*  Evaluate the polynomial poly of the length len at the specified value. */
+double polyval(construct *poly, double value, size_t len)
+{
+	if (!len--)
+		return 0;
+	double coeff = *(double *) car(poly);
+	return pow(value, len) * coeff + polyval(cdr(poly), value, len);
+}
+
+/* Print the polynomial poly of the length len using the specified varname. */
+void polyprint(construct *poly, char *varname, size_t len)
+{
+	if (len--) {
+		printf(len ? "%g%s^%zu + " : "%g",
+		       *(double *) car(poly), varname, len);
+		polyprint(cdr(poly), varname, len);
+	} else {
+		putchar(10);
+	}
+}
+
+int main()
+{
+	construct *polynomial = NULL;
+	srand(time(NULL));
+	int len = rand() % 4 + 3;
+
+	for (int i = 0; i < len; ++i) {
+		double *coeff = malloc(sizeof(double));
+		*coeff = rand() % COEFF_MOD;
+		polynomial = cons(coeff, polynomial);
+	}
+
+	puts("Initial polynomial:");
+	polyprint(polynomial, "x", len);
+
+	double x = rand() % COEFF_MOD;
+	int n = rand() % len;
+	polynomial = add_term(polynomial, x, n);
+	printf("The polynomial after adding %g to the number %d term:\n", x, n);
+	polyprint(polynomial, "x", len);
+
+	polynomial = remove_term(polynomial, --len);
+	printf("The polynomial after removing the number %d term:\n", len);
+	polyprint(polynomial, "x", len);
+
+	n = rand() % (len - 1);
+	polynomial = remove_term(polynomial, n);
+	printf("The polynomial after removing the number %d term:\n", n);
+	polyprint(polynomial, "x", len);
+
+	puts("Evaluation of the polynomial using x from stdin:");
+	scanf("%lf", &x);
+	printf("%g\n", polyval(polynomial, x, len));
+
+	return 0;
+}
diff --git a/usth/ICT2.1/labwork/2/README.md b/usth/ICT2.1/labwork/2/README.md
new file mode 100644
index 0000000..25b43c4
--- /dev/null
+++ b/usth/ICT2.1/labwork/2/README.md
@@ -0,0 +1,49 @@
+# Algorithms and Data Structures: Tutorial 2
+
+This package contains the following files:
+
+* construct.h
+* construct.c
+* Ex1.c
+* Ex2.c
+
+Where construct is an minimal implementation of Lisp construct with
+`cons`, `car`, `cdr`, `length`, `nth` and `insert`.  It eases and simplifies
+the implementation of linked lists (and trees and and graphs if we study them
+later on).  All source files are as licensed under the Unlicense which states
+
+> This is free and unencumbered software released into the public domain.
+>
+> Anyone is free to copy, modify, publish, use, compile, sell, or
+> distribute this software, either in source code form or as a compiled
+> binary, for any purpose, commercial or non-commercial, and by any
+> means.
+>
+> In jurisdictions that recognize copyright laws, the author or authors
+> of this software dedicate any and all copyright interest in the
+> software to the public domain. We make this dedication for the benefit
+> of the public at large and to the detriment of our heirs and
+> successors. We intend this dedication to be an overt act of
+> relinquishment in perpetuity of all present and future rights to this
+> software under copyright law.
+>
+> THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+> EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+> MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
+> IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR
+> OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
+> ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
+> OTHER DEALINGS IN THE SOFTWARE.
+>
+> For more information, please refer to <http://unlicense.org/>
+
+The solution of the second exercise uses the math library and thus
+it needs to by linked during compilation.  Both uses the `construct` library:
+
+    cc construct.c Ex1.c -o Ex1
+    cc construct.c Ex2.c -lm -o Ex2
+
+Additionally, `Ex2` requires a value of `x` to be entered from stdin:
+
+    ./Ex1
+    echo 7 | ./Ex2
diff --git a/usth/ICT2.1/labwork/2/TT2.pdf b/usth/ICT2.1/labwork/2/TT2.pdf
new file mode 100644
index 0000000..c373df5
--- /dev/null
+++ b/usth/ICT2.1/labwork/2/TT2.pdf
Binary files differdiff --git a/usth/ICT2.1/labwork/2/construct.c b/usth/ICT2.1/labwork/2/construct.c
new file mode 100644
index 0000000..db32d8a
--- /dev/null
+++ b/usth/ICT2.1/labwork/2/construct.c
@@ -0,0 +1,57 @@
+/*
+ * Lisp construct implementation.
+ * This is free and unencumbered software released into the public domain.
+ */
+
+#include <stdlib.h>
+
+#include "construct.h"
+
+construct *cons(void *first, construct *rest)
+{
+	construct *list = malloc(sizeof(construct));
+	list->car = first;
+	list->cdr = rest;
+	return list;
+}
+
+void *car(construct *list)
+{
+	return list->car;
+}
+
+construct *cdr(construct *list)
+{
+	return list->cdr;
+}
+
+size_t length(construct *list)
+{
+	if (list == NULL)
+		return 0;
+	return length(cdr(list)) + 1;
+}
+
+void *nth(construct *list, size_t n)
+{
+	if (list == NULL)
+		return NULL;
+	return n ? nth(cdr(list), n - 1) : car(list);
+}
+
+/*
+ * Try to insert x before item of index i and return the new construct.
+ * Return NULL on invalid index.
+ */
+construct *insert(void *x, construct *list, size_t i)
+{
+	if (!i)
+		return cons(x, list);
+	if (list == NULL)
+		return NULL;
+
+	void *first = car(list);
+	construct *rest = cdr(list);
+	free(list);
+	return cons(first, insert(x, rest, i - 1));
+}
diff --git a/usth/ICT2.1/labwork/2/construct.h b/usth/ICT2.1/labwork/2/construct.h
new file mode 100644
index 0000000..2d1c840
--- /dev/null
+++ b/usth/ICT2.1/labwork/2/construct.h
@@ -0,0 +1,17 @@
+/*
+ * Lisp construct header.
+ * This is free and unencumbered software released into the public domain.
+ */
+
+typedef struct list construct;
+struct list {
+	void *car;
+        construct *cdr;
+};
+
+construct *cons(void *, construct *);
+void *car(construct *);
+construct *cdr(construct *);
+size_t length(construct *);
+void *nth(construct *, size_t);
+construct *insert(void *, construct *, size_t);
diff --git a/usth/ICT2.1/labwork/3/Ex1.c b/usth/ICT2.1/labwork/3/Ex1.c
new file mode 100644
index 0000000..90b3ca5
--- /dev/null
+++ b/usth/ICT2.1/labwork/3/Ex1.c
@@ -0,0 +1,38 @@
+/*
+ * Reverse name from stdin.
+ * This is free and unencumbered software released into the public domain.
+ */
+
+#include <ctype.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+#include "stack.h"
+
+int main()
+{
+	stack *s = mkstack();
+	char c, *p;
+
+	while ((c = getchar()) != EOF) {
+		p = malloc(sizeof(char *));
+		*p = isspace(c) ? 32 : c;
+		stack_push(s, p);
+	}
+
+	while (!stack_empty(s) && *(char *) stack_top(s) == 32) {
+		p = stack_pop(s);
+		free(p);
+	}
+
+	c = 32;
+	while (!stack_empty(s)) {
+		p = stack_pop(s);
+		putchar(c == 32 ? toupper(c = *p) : tolower(c = *p));
+		free(p);
+	}
+
+	putchar(10);
+
+	return 0;
+}
diff --git a/usth/ICT2.1/labwork/3/Ex2.c b/usth/ICT2.1/labwork/3/Ex2.c
new file mode 100644
index 0000000..49be21b
--- /dev/null
+++ b/usth/ICT2.1/labwork/3/Ex2.c
@@ -0,0 +1,61 @@
+/*
+ * Add hard-coded names to a queue a print them to stdout.
+ * This is free and unencumbered software released into the public domain.
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+
+#include "construct.h"
+
+typedef struct {
+	construct *front;
+	construct *rear;
+} queue;
+
+queue *mkq()
+{
+	queue *q = malloc(sizeof(queue));
+	q->front = q->rear = NULL;
+}
+
+int qempty(queue *q)
+{
+	return q->front == NULL;
+}
+
+void qpush(queue *q, void *item)
+{
+	if (qempty(q))
+		q->front = q->rear = cons(item, NULL);
+	else
+		q->rear = q->rear->cdr = cons(item, NULL);
+}
+
+void *qpop(queue *q)
+{
+	if (qempty(q))
+		return NULL;
+	void *first = car(q->front);
+	construct *rest = cdr(q->front);
+	free(q->front);
+	q->front = rest;
+	return first;
+}
+
+int main()
+{
+	queue *q = mkq();	
+	qpush(q, "Mahathir Mohamad");
+	qpush(q, "Elizabeth II");
+	qpush(q, "Sheikh Sabah Al-Ahmad Al-Jaber Al-Sabah");
+	qpush(q, "Paul Biya");
+	qpush(q, "Michel Aoun");
+	qpush(q, "Mahmoud Abbas");
+	qpush(q, "Francis");
+
+	while (!qempty(q))
+		puts(qpop(q));
+
+	return 0;
+}
diff --git a/usth/ICT2.1/labwork/3/Ex3.c b/usth/ICT2.1/labwork/3/Ex3.c
new file mode 100644
index 0000000..b934ec0
--- /dev/null
+++ b/usth/ICT2.1/labwork/3/Ex3.c
@@ -0,0 +1,46 @@
+/*
+ * Interactive guessing game.
+ * This is free and unencumbered software released into the public domain.
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <time.h>
+
+#include "stack.h"
+
+char *random10(char *c)
+{
+	char *p = malloc(sizeof(char));
+	*p = rand() % 10;
+	while (c != NULL && *p == *c) {
+		free(p);
+		p = malloc(sizeof(char));
+		*p = rand() % 10;
+	}
+	return p;
+}
+
+int main()
+{
+	stack *s = mkstack();
+	char guess, lost = 0;
+	srand(time(NULL));
+	stack_push(s, random10(NULL));
+STEP2:
+	stack_push(s, random10(stack_top(s)));
+	char *p = stack_pop(s);
+	puts(lost ? "Make another guess between 0 and 9"
+		  : "Make a guess between 0 and 9");
+	scanf("%hhd", &guess);
+	if ((guess - *p) * (guess - *(char *) stack_top(s)) < 0) {
+		puts("YOU WIN!");
+		return 0;
+	} else if (lost) {
+		puts("YOU LOSE!");
+		return 0;
+	}
+	
+	lost = 1;
+	goto STEP2;
+}
diff --git a/usth/ICT2.1/labwork/3/README.md b/usth/ICT2.1/labwork/3/README.md
new file mode 100644
index 0000000..a38ee6e
--- /dev/null
+++ b/usth/ICT2.1/labwork/3/README.md
@@ -0,0 +1,42 @@
+# Algorithms and Data Structures: Tutorial 3
+
+This package contains the following files:
+
+* `construct.h`, `construct.c`: Lisp construct (with `cons`, `car` and `cdr`)
+* `stack.h`, `stack.c`: initialization, check for empty, push, top and pop
+* `Ex1.c`: read from stdin and reverse the name
+* `Ex2.c`: add hard-coded names to a queue a print them to stdout
+* `Ex3.c`: interactive guessing game
+
+Compilation can be done as follows
+
+    cc construct.c stack.c Ex1.c -o Ex1
+    cc construct.c Ex2.c -o Ex2
+    cc construct.c stack.c Ex3.c -o Ex3
+
+All source files are as licensed under the Unlicense which states
+
+> This is free and unencumbered software released into the public domain.
+>
+> Anyone is free to copy, modify, publish, use, compile, sell, or
+> distribute this software, either in source code form or as a compiled
+> binary, for any purpose, commercial or non-commercial, and by any
+> means.
+>
+> In jurisdictions that recognize copyright laws, the author or authors
+> of this software dedicate any and all copyright interest in the
+> software to the public domain. We make this dedication for the benefit
+> of the public at large and to the detriment of our heirs and
+> successors. We intend this dedication to be an overt act of
+> relinquishment in perpetuity of all present and future rights to this
+> software under copyright law.
+>
+> THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+> EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+> MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
+> IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR
+> OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
+> ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
+> OTHER DEALINGS IN THE SOFTWARE.
+>
+> For more information, please refer to <http://unlicense.org/>
diff --git a/usth/ICT2.1/labwork/3/TT3.pdf b/usth/ICT2.1/labwork/3/TT3.pdf
new file mode 100644
index 0000000..708d20a
--- /dev/null
+++ b/usth/ICT2.1/labwork/3/TT3.pdf
Binary files differdiff --git a/usth/ICT2.1/labwork/3/construct.c b/usth/ICT2.1/labwork/3/construct.c
new file mode 100644
index 0000000..887b6d8
--- /dev/null
+++ b/usth/ICT2.1/labwork/3/construct.c
@@ -0,0 +1,26 @@
+/*
+ * Lisp construct implementation.
+ * This is free and unencumbered software released into the public domain.
+ */
+
+#include <stdlib.h>
+
+#include "construct.h"
+
+construct *cons(void *first, construct *rest)
+{
+	construct *list = malloc(sizeof(construct));
+	list->car = first;
+	list->cdr = rest;
+	return list;
+}
+
+void *car(construct *list)
+{
+	return list->car;
+}
+
+construct *cdr(construct *list)
+{
+	return list->cdr;
+}
diff --git a/usth/ICT2.1/labwork/3/construct.h b/usth/ICT2.1/labwork/3/construct.h
new file mode 100644
index 0000000..35d2448
--- /dev/null
+++ b/usth/ICT2.1/labwork/3/construct.h
@@ -0,0 +1,14 @@
+/*
+ * Lisp construct header.
+ * This is free and unencumbered software released into the public domain.
+ */
+
+typedef struct list construct;
+struct list {
+	void *car;
+        construct *cdr;
+};
+
+construct *cons(void *, construct *);
+void *car(construct *);
+construct *cdr(construct *);
diff --git a/usth/ICT2.1/labwork/3/stack.c b/usth/ICT2.1/labwork/3/stack.c
new file mode 100644
index 0000000..708fb59
--- /dev/null
+++ b/usth/ICT2.1/labwork/3/stack.c
@@ -0,0 +1,39 @@
+/*
+ * Stack implemented using linked list.
+ * This is free and unencumbered software released into the public domain.
+ */
+
+#include <stdlib.h>
+
+#include "stack.h"
+
+stack *mkstack()
+{
+	stack *s = malloc(sizeof(stack));
+	s->stack = NULL;
+	return s;
+}
+
+int stack_empty(stack *s)
+{
+	return s->stack == NULL;
+}
+
+void stack_push(stack *s, void *item)
+{
+	s->stack = cons(item, s->stack);
+}
+
+void *stack_top(stack *s)
+{
+	return car(s->stack);
+}
+
+void *stack_pop(stack *s)
+{
+	void *first = car(s->stack);
+	construct *rest = cdr(s->stack);
+	free(s->stack);
+	s->stack = rest;
+	return first;
+}
diff --git a/usth/ICT2.1/labwork/3/stack.h b/usth/ICT2.1/labwork/3/stack.h
new file mode 100644
index 0000000..2ed8851
--- /dev/null
+++ b/usth/ICT2.1/labwork/3/stack.h
@@ -0,0 +1,16 @@
+/*
+ * Stack header.
+ * This is free and unencumbered software released into the public domain.
+ */
+
+#include "construct.h"
+
+typedef struct {
+	construct *stack;
+} stack;
+
+stack *mkstack();
+int stack_empty(stack *);
+void stack_push(stack *, void *);
+void *stack_top(stack *);
+void *stack_pop(stack *);
diff --git a/usth/ICT2.1/labwork/4/Bonus.c b/usth/ICT2.1/labwork/4/Bonus.c
new file mode 100644
index 0000000..b46b3fe
--- /dev/null
+++ b/usth/ICT2.1/labwork/4/Bonus.c
@@ -0,0 +1,26 @@
+/*
+ * Solve Towers of Hà Nội of height n, where towers are named foo, bar and baz.
+ * This is free and unencumbered software released into the public domain.
+ */
+
+#include <stdio.h>
+
+void anoi(unsigned n, char *one, char *other, char *another)
+{
+	if (n == 0)
+		return;
+
+	anoi(n - 1, one, another, other);
+	printf("Move from %s to %s\n", one, other);
+	anoi(n - 1, another, other, one);
+}
+
+int main()
+{
+	unsigned n;
+
+	scanf("%u", &n);
+	anoi(n, "foo", "bar", "baz");
+
+	return 0;
+}
diff --git a/usth/ICT2.1/labwork/4/Ex1.c b/usth/ICT2.1/labwork/4/Ex1.c
new file mode 100644
index 0000000..4d0ab5d
--- /dev/null
+++ b/usth/ICT2.1/labwork/4/Ex1.c
@@ -0,0 +1,25 @@
+/*
+ * Multiply two natural numbers from stdin and print the result to stdout.
+ * This is free and unencumbered software released into the public domain.
+ */
+
+#include <stdio.h>
+
+int multiply(int a, int b)
+{
+	if (a > 0)
+		return multiply(a - 1, b) + b;
+	if (a < 0)
+		return multiply(a + 1, b) - b;
+	return 0;
+}
+
+int main()
+{
+	int a, b;
+
+	scanf("%d %d", &a, &b);
+	printf("%d\n", multiply(a, b));
+
+	return 0;
+}
diff --git a/usth/ICT2.1/labwork/4/Ex2.c b/usth/ICT2.1/labwork/4/Ex2.c
new file mode 100644
index 0000000..6ad6b87
--- /dev/null
+++ b/usth/ICT2.1/labwork/4/Ex2.c
@@ -0,0 +1,46 @@
+/*
+ * Read n from stdin and print all primes from 1 to n to stdout.
+ * This is free and unencumbered software released into the public domain.
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+
+void subsieve(int *mask, int n, int i, int j)
+{
+	if (j > n)
+		return;
+	mask[j] = 1;
+	subsieve(mask, n, i, i + j);
+}
+
+void sieve(int *mask, int n, int i)
+{
+	if (i * i > n)
+		return;
+	if (!mask[i])
+		subsieve(mask, n, i, i + i);
+	sieve(mask, n, i + 1);
+}
+
+void print_primes(int *mask, int n)
+{
+	if (!n)
+		return;
+	if (!mask[n])
+		printf("%d\n", n);
+	print_primes(mask, n - 1);
+}
+
+int main()
+{
+	int n;
+	scanf("%d", &n);
+
+	int *notprime = calloc(n + 1, sizeof(int));
+	notprime[0] = notprime[1] = 1;
+	sieve(notprime, n, 2);
+	print_primes(notprime, n);
+
+	return 0;
+}
diff --git a/usth/ICT2.1/labwork/4/Ex3.c b/usth/ICT2.1/labwork/4/Ex3.c
new file mode 100644
index 0000000..ba016fc
--- /dev/null
+++ b/usth/ICT2.1/labwork/4/Ex3.c
@@ -0,0 +1,32 @@
+/*
+ * Read numbers from stdin to a link list and print their sum to stdout.
+ * This is free and unencumbered software released into the public domain.
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+
+#include "construct.h"
+
+construct *readoubles()
+{
+	double *x = malloc(sizeof(double));
+	if (scanf("%lf", x) != EOF)
+		return cons(x, readoubles());
+	free(x);
+	return NULL;
+}
+
+double sum(construct *list)
+{
+	if (list == NULL)
+		return 0.0;
+	/* At program termination the memory will be freed anyway. */
+	return *(double *) car(list) + sum(cdr(list));
+}
+
+int main()
+{
+	printf("%g\n", sum(readoubles()));
+	return 0;
+}
diff --git a/usth/ICT2.1/labwork/4/Ex4.c b/usth/ICT2.1/labwork/4/Ex4.c
new file mode 100644
index 0000000..86eaabb
--- /dev/null
+++ b/usth/ICT2.1/labwork/4/Ex4.c
@@ -0,0 +1,34 @@
+/*
+ * Exchange money from stdin to least number of 1, 2, 5, 10, 20 and 50 bills.
+ * This is free and unencumbered software released into the public domain.
+ */
+
+#include <stdio.h>
+
+struct change {
+	unsigned amount, bill;
+};
+
+const unsigned BILLS[] = {50, 20, 10, 5, 2, 1, 0};
+
+void print_exchange(unsigned money, const unsigned *bills)
+{
+	if (!*bills)
+		return;
+	if (*bills > money) {
+		print_exchange(money, bills + 1);
+		return;
+	}
+	printf("%u %u\n", money / *bills, *bills);
+	print_exchange(money % *bills, bills + 1);
+}
+
+int main()
+{
+	unsigned n;
+
+	scanf("%u", &n);
+	print_exchange(n, BILLS);
+
+	return 0;
+}
diff --git a/usth/ICT2.1/labwork/4/README.md b/usth/ICT2.1/labwork/4/README.md
new file mode 100644
index 0000000..a7d0eee
--- /dev/null
+++ b/usth/ICT2.1/labwork/4/README.md
@@ -0,0 +1,46 @@
+# Algorithms and Data Structures: Tutorial 4
+
+This package contains the following files:
+
+* `construct.h`, `construct.c`: Lisp construct (with `cons`, `car` and `cdr`)
+* `Ex1.c`: take 2 integers from stdin and print there product to stdout
+* `Ex2.c`: print all primes in 1..n to stdout with n from stdin
+* `Ex3.c`: print to stdout the sum of elements from stdin
+* `Ex4.c`: exchange given amount of money from stdin to least number
+  of [1 2 5 10 20 50] bills and print the pairs of (amount, bill) to stdout
+* `Bonus.c`: Towers of Hà Nội problem: no link list or stack needed
+
+Compilation can be done as follows
+
+    cc Ex1.c -o Ex1
+    cc Ex2.c -o Ex2
+    cc construct.c Ex3.c -o Ex3
+    cc Ex4.c -o Ex4
+    cc Bonus.c -o Bonus
+
+All source files are as licensed under the Unlicense which states
+
+> This is free and unencumbered software released into the public domain.
+>
+> Anyone is free to copy, modify, publish, use, compile, sell, or
+> distribute this software, either in source code form or as a compiled
+> binary, for any purpose, commercial or non-commercial, and by any
+> means.
+>
+> In jurisdictions that recognize copyright laws, the author or authors
+> of this software dedicate any and all copyright interest in the
+> software to the public domain. We make this dedication for the benefit
+> of the public at large and to the detriment of our heirs and
+> successors. We intend this dedication to be an overt act of
+> relinquishment in perpetuity of all present and future rights to this
+> software under copyright law.
+>
+> THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+> EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+> MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
+> IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR
+> OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
+> ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
+> OTHER DEALINGS IN THE SOFTWARE.
+>
+> For more information, please refer to <http://unlicense.org/>
diff --git a/usth/ICT2.1/labwork/4/TT4.pdf b/usth/ICT2.1/labwork/4/TT4.pdf
new file mode 100644
index 0000000..630172e
--- /dev/null
+++ b/usth/ICT2.1/labwork/4/TT4.pdf
Binary files differdiff --git a/usth/ICT2.1/labwork/4/construct.c b/usth/ICT2.1/labwork/4/construct.c
new file mode 100644
index 0000000..887b6d8
--- /dev/null
+++ b/usth/ICT2.1/labwork/4/construct.c
@@ -0,0 +1,26 @@
+/*
+ * Lisp construct implementation.
+ * This is free and unencumbered software released into the public domain.
+ */
+
+#include <stdlib.h>
+
+#include "construct.h"
+
+construct *cons(void *first, construct *rest)
+{
+	construct *list = malloc(sizeof(construct));
+	list->car = first;
+	list->cdr = rest;
+	return list;
+}
+
+void *car(construct *list)
+{
+	return list->car;
+}
+
+construct *cdr(construct *list)
+{
+	return list->cdr;
+}
diff --git a/usth/ICT2.1/labwork/4/construct.h b/usth/ICT2.1/labwork/4/construct.h
new file mode 100644
index 0000000..35d2448
--- /dev/null
+++ b/usth/ICT2.1/labwork/4/construct.h
@@ -0,0 +1,14 @@
+/*
+ * Lisp construct header.
+ * This is free and unencumbered software released into the public domain.
+ */
+
+typedef struct list construct;
+struct list {
+	void *car;
+        construct *cdr;
+};
+
+construct *cons(void *, construct *);
+void *car(construct *);
+construct *cdr(construct *);
diff --git a/usth/ICT2.1/labwork/5/Ex1.c b/usth/ICT2.1/labwork/5/Ex1.c
new file mode 100644
index 0000000..e64c6ea
--- /dev/null
+++ b/usth/ICT2.1/labwork/5/Ex1.c
@@ -0,0 +1,58 @@
+/*
+ * Cocktail shaker sorting integers from stdin
+ * Copyright (C) 2019,  Nguyễn Gia Phong
+ * This software is licenced under a CC BY-SA 4.0 license
+ */
+
+#include <stdio.h>
+
+void strswap(char *this, char *that, size_t n)
+{
+	while (n--) {
+		this[n] ^= that[n];
+		that[n] ^= this[n];
+		this[n] ^= that[n];
+	}
+}
+
+void csort(void *base, size_t nmemb, size_t size,
+           int (*compar)(const void *, const void *))
+{
+	char *i, *low = base;
+	char *high = low + nmemb * size;
+	do {
+		char *h = i = low;
+		while ((i += size) < high)
+			if (compar(i - size, i) > 0)
+				strswap(i - size, h = i, size);
+		high = h;
+		if (low + size >= high)
+			break;
+		char *l = i = high;
+		while ((i -= size) > low)
+			if (compar(i - size, i) > 0)
+				strswap(i - size, l = i, size);
+		low = l;
+	} while (low + size < high);
+}
+
+int cmp(const void *x, const void *y)
+{
+	return *(int *) x - *(int *) y;
+}
+
+int main()
+{
+	size_t n;
+	scanf("%zu", &n);
+	int a[n];
+	for (int i = 0; i < n; i++)
+		scanf("%d", a + i);
+
+	csort(a, n, sizeof(int), cmp);
+	for (int i = 0; i < n; i++)
+		printf("%d ", a[i]);
+	putchar(10);
+
+	return 0;
+}
diff --git a/usth/ICT2.1/labwork/5/Ex2.c b/usth/ICT2.1/labwork/5/Ex2.c
new file mode 100644
index 0000000..edb5c26
--- /dev/null
+++ b/usth/ICT2.1/labwork/5/Ex2.c
@@ -0,0 +1,74 @@
+/*
+ * Merge sorting integers from stdin
+ * Copyright (C) 2019,  Nguyễn Gia Phong
+ * This software is licenced under a CC BY-SA 4.0 license
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+
+#include "construct.h"
+
+construct *merge(construct *left, construct *right,
+                 int (*compar)(const void *, const void *))
+{
+	if (left == NULL)
+		return right;
+	if (right == NULL)
+		return left;
+	if (compar(car(left), car(right)) <= 0)
+		return cons(car(left), merge(cdr(left), right, compar));
+	return cons(car(right), merge(left, cdr(right), compar));
+}
+
+construct *msort(construct *list, int (*compar)(const void *, const void *))
+{
+	construct *rest, *left = NULL, *right = NULL;
+	while (list != NULL) {
+		left = cons(car(list), left);
+		rest = cdr(list);
+		if (rest == NULL)
+			break;
+		right = cons(car(rest), right);
+		list = cdr(rest);
+	}
+	if (left == NULL)
+		return right;
+	if (right == NULL)
+		return left;
+	return merge(msort(left, compar), msort(right, compar), compar);
+}
+
+int cmp(const void *x, const void *y)
+{
+	return *(int *) x - *(int *) y;
+}
+
+construct *iread(size_t n)
+{
+	if (!n)
+		return NULL;
+	int *tmp = malloc(sizeof(int));
+	scanf("%d", tmp);
+	return cons(tmp, iread(n - 1));
+}
+
+void iprint(construct *list)
+{
+	if (list == NULL) {
+		putchar(10);
+	} else {
+		printf("%d ", *(int *) car(list));
+		iprint(cdr(list));
+	}
+}
+
+int main()
+{
+	size_t n;
+
+	scanf("%zu", &n);
+	iprint(msort(iread(n), cmp));
+
+	return 0;
+}
diff --git a/usth/ICT2.1/labwork/5/README.pdf b/usth/ICT2.1/labwork/5/README.pdf
new file mode 100644
index 0000000..8a94167
--- /dev/null
+++ b/usth/ICT2.1/labwork/5/README.pdf
Binary files differdiff --git a/usth/ICT2.1/labwork/5/README.tex b/usth/ICT2.1/labwork/5/README.tex
new file mode 100644
index 0000000..4c71999
--- /dev/null
+++ b/usth/ICT2.1/labwork/5/README.tex
@@ -0,0 +1,143 @@
+\documentclass[a4paper,12pt]{article}
+\usepackage[english,vietnamese]{babel}
+\usepackage{amsmath}
+\usepackage{hyperref}
+\usepackage{lmodern}
+\usepackage{mathtools}
+
+\title{Algorithms and Data Structures\\ Searching and Sorting}
+\author{Nguyễn Gia Phong---BI9-184}
+\date{\dateenglish\today}
+
+\begin{document}
+\maketitle
+\section{Cocktail Shaker Sort}
+The code is implemented following the cocktail shaker sort's
+pseudocode\footnote{\url{https://en.wikipedia.org/wiki/Cocktail\_shaker\_sort\#Pseudocode}}
+with bubble sort's optimization\footnote{\url{https://en.wikipedia.org/wiki/Bubble\_sort\#Optimizing\_bubble\_sort}}
+whose time complexity is analyzed as follows
+
+\subsection{Best Case}
+For the matter of brevity, we consider all operations on the array's $n$ members
+are in constant time ($\Theta(1)$).  If the array is already sorted, after
+the first \verb|while| loop (line 25), \verb|h| is still \verb|low| and thus
+the \verb|do|--\verb|while| loop is broken.  Since the while loop runs from
+\verb|low + size| to \verb|high - size| by \verb|size| steps, the running time
+is \verb|(high - low - size*2)/size + 1| or \verb|nmemb - 1|.  Therefore
+the best case time complexity is $\Omega(n - 1) = \Omega(n)$.
+
+\subsection{Average Case}
+Assume the average case is when the array is uniformly shuffled, that is,
+every permutation has the equal probability to occur.
+
+Given a permutation of an $n$-element array, consider the positive integer
+$k \le n$ that exactly the last $n - k$ members are continuously in the
+correct positions (as in the ascendingly sorted array).  It is obvious that
+for $k = 1$, the array is sorted and the probability of the permutation
+to appear is $1/n!$.  For $1 < k \le n$, if we fix the last $n - k$ members
+in their right places, out of the $k!$ permutations of the first $k$ elements,
+$(k - 1)!$ ones has the $k$-th greatest at the correct place.  Therefore,
+let $X$ be the number that exactly $n - X$ last elements are in
+the right positions, we have
+\[p_X(k) = \begin{dcases}
+  \frac{1}{n!} &\text{if }k = 1\\
+  \frac{k! - (k - 1)!}{n!} &\text{otherwise}
+\end{dcases}\]
+
+Applying this to the first \verb|while| (line 25) with $n$ and $X - 1$ being
+the number of steps from \verb|low| to \verb|high|, before and after
+\verb|high = h| respectively, the expectation of $X$ is
+\begin{align*}
+  \mathbf E[X] &= \sum_{k=1}^n k p_X(k)\\
+  &= \frac{1}{n!} + \sum_{k=2}^n\frac{k!k - k!}{n!}\\
+  &= \frac{1}{n!} + \sum_{k=3}^{n+1}\frac{k!}{n!}
+   - \sum_{k=2}^n\frac{k!}{n!} - \sum_{k=2}^n\frac{k!}{n!}\\
+  &= \frac{1}{n!} + \frac{(n+1)!}{n!}
+   - \frac{2!}{n!} - \sum_{k=2}^n\frac{k!}{n!}\\
+  &= n + 1 - \sum_{k=1}^n\frac{k!}{n!}\\
+  &= n - \sum_{k=1}^{n-1}\frac{k!}{n!}
+\end{align*}
+
+Hence after line 28, the newly sorted length of the array is
+\[n - \mathbf E[X - 1] = n - \mathbf E[X] + 1
+  = 1 + \sum_{k=1}^{n-1}\frac{k!}{n!} = \Theta(1)\]
+
+Similarly, line 31 to 35 also sort $\Theta(1)$ element(s), thus each iteration
+of the \verb|do|--\verb|while| loop to sort $\Theta(1)$ members. The overall
+average-case time complexity is
+\begin{align*}
+  T(n) &= \begin{dcases}
+    (n - \Theta(1)) + (n - \Theta(1)) + T(n - \Theta(1)) &\text{if }n > 0\\
+    \Theta(1) &\text{otherwise}
+  \end{dcases}\\
+  &= \begin{dcases}
+    2n - \Theta(1) + T(n - \Theta(1)) &\text{if }n > 0\\
+    \Theta(1) &\text{otherwise}
+  \end{dcases}\\
+  &= \Theta(1) + \sum_{k=1}^m(2k - \Theta(1))
+  = 2\sum_{k=1}^m k - \sum_{k=1}^m\Theta(1)
+  = m^2 + m - \sum_{k=1}^m\Theta(1)
+\end{align*}
+where $m$ satisfies
+\begin{multline*}
+  \exists\{f_k\mid k\in 1\,..\,m\} \subset \Theta(1),\,
+  \sum_{k=1}^m f_k(n) = n
+  \Longrightarrow \sum_{k=1}^m\Theta(1) = \Theta(n)
+  \Longrightarrow m = \Theta(n)\\
+  \Longrightarrow T(n) = \Theta\left(n^2\right) + \Theta(n) - \Theta(n)
+  = \Theta\left(n^1\right)
+\end{multline*}
+
+\subsection{Worst Case}
+If the array is reversely sorted, after each first \verb|while| (line 25),
+\verb|high| is decreased by \verb|size|; and after each second
+\verb|while| (line 32), \verb|low| is increased by \verb|size|.
+For \verb|low + size >= high|, it takes \verb|(high-low-size)/size + 1 >> 1|
+or \verb|nmemb / 2| iterations of the \verb|do|--\verb|while| loop (line 23).
+The overall complexity would then be
+\begin{align*}
+  \sum_{k=1}^{\lfloor n/2\rfloor}(n - 2k + 1 + n - 2k)
+  &= \sum_{k=1}^{\lfloor n/2\rfloor}(2n - 4k + 1)\\
+  &= n^2 + 2\left\lfloor\frac{n}{2}\right\rfloor
+  \left(\left\lfloor\frac{n}{2}\right\rfloor + 1\right)
+  + \left\lfloor\frac{n}{2}\right\rfloor\\
+  &= O\left(n^2\right)
+\end{align*}
+
+\section{Merge Sort}
+As usual, the linked list is implemented using classic Lisp's \verb|cons|-cells.
+The program is thus compiled by
+\begin{verbatim}
+cc construct.c Ex2.c -o Ex2
+\end{verbatim}
+
+To keep the implementation concise, memory safety as well as stack limit
+was not considered.
+
+It is trivial that the time complexity of \verb|merge| is $\Theta(n)$ with
+$n$ being the total length of \verb|left| and \verb|right|.  For \verb|msort|,
+the running time of the \verb|while| loop at line 27 is also $\Theta(n)$, where
+n is the length of the input \verb|list|.  The overall time complexity is
+\[T(n) = \begin{dcases}
+  \Theta(1) &\text{if }n \le 1\\
+  \Theta(n) + T\left(\left\lfloor\frac{n}{2}\right\rfloor\right)
+  + T\left(\left\lceil\frac{n}{2}\right\rceil\right) &\text{otherwise}
+\end{dcases}\]
+
+The recurrence can be stated as
+\[T(n) = 2T\left(\frac{n}{2}\right) + \Theta(n)\]
+\pagebreak
+
+By the master theorem\footnote{Let $a \ge 1$ and $b > 1$ be constants,
+and let $T(n)$ be defined on the nonnegative integers by the recurrence
+\[T(n) = aT\left(\frac{n}{b}\right) + \Theta\left(n^{\log_b a}\right)\]
+where $n/b$ is interpreted as either $\lfloor n/b\rfloor$ or $\lceil n/b\rceil$,
+then \[T(n) = \Theta\left(n^{\log_b a}\lg n\right)\]},
+\[T(n) = 2T\left(\frac{n}{2}\right) + \Theta\left(n^{\log_2 2}\right)
+= \Theta\left(n^{\log_2 2}\lg n\right) = \Theta(n\lg n)\]
+
+\section{Copying}
+This report along with the source files are licensed under a
+\href{https://creativecommons.org/licenses/by-sa/4.0/}{Creative Commons
+Attribution-ShareAlike 4.0 International License}.
+\end{document}
diff --git a/usth/ICT2.1/labwork/5/TT5.pdf b/usth/ICT2.1/labwork/5/TT5.pdf
new file mode 100644
index 0000000..1038597
--- /dev/null
+++ b/usth/ICT2.1/labwork/5/TT5.pdf
Binary files differdiff --git a/usth/ICT2.1/labwork/5/construct.c b/usth/ICT2.1/labwork/5/construct.c
new file mode 100644
index 0000000..235f900
--- /dev/null
+++ b/usth/ICT2.1/labwork/5/construct.c
@@ -0,0 +1,27 @@
+/*
+ * Lisp construct implementation.
+ * Copyright (C) 2019,  Nguyễn Gia Phong
+ * This software is licenced under a CC BY-SA 4.0 license
+ */
+
+#include <stdlib.h>
+
+#include "construct.h"
+
+construct *cons(void *first, construct *rest)
+{
+	construct *list = malloc(sizeof(construct));
+	list->car = first;
+	list->cdr = rest;
+	return list;
+}
+
+void *car(construct *list)
+{
+	return list->car;
+}
+
+construct *cdr(construct *list)
+{
+	return list->cdr;
+}
diff --git a/usth/ICT2.1/labwork/5/construct.h b/usth/ICT2.1/labwork/5/construct.h
new file mode 100644
index 0000000..a27a1c3
--- /dev/null
+++ b/usth/ICT2.1/labwork/5/construct.h
@@ -0,0 +1,15 @@
+/*
+ * Lisp construct header.
+ * Copyright (C) 2019,  Nguyễn Gia Phong
+ * This software is licenced under a CC BY-SA 4.0 license
+ */
+
+typedef struct list construct;
+struct list {
+	void *car;
+        construct *cdr;
+};
+
+construct *cons(void *, construct *);
+void *car(construct *);
+construct *cdr(construct *);
diff --git a/usth/ICT2.1/labwork/6/Ex1.c b/usth/ICT2.1/labwork/6/Ex1.c
new file mode 100644
index 0000000..12ebb02
--- /dev/null
+++ b/usth/ICT2.1/labwork/6/Ex1.c
@@ -0,0 +1,123 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <time.h>
+
+#define MIN(a, b) (((a) < (b)) ? (a) : (b))
+#define MAX(a, b) (((a) > (b)) ? (a) : (b))
+
+int *rand_array(size_t nmemb)
+{
+	int *base = malloc(nmemb * sizeof(int));
+	for (size_t i = 0; i < nmemb; ++i)
+		base[i] = rand() % (1 << nmemb);
+	return base;
+}
+
+size_t bits(size_t n)
+{
+	size_t h = 0;
+	while (n) {
+		n >>= 1;
+		h++;
+	}
+	return h;
+}
+
+void *tree(int *base, size_t *nmemb)
+{
+	size_t n = 1 << bits(*nmemb - 1);
+	if ((base = realloc(base, n * sizeof(int) << 1)) == NULL)
+		return NULL;
+	memcpy(base + n, base, *nmemb * sizeof(int));
+	int max = *base;
+	for (size_t i = 1; i < *nmemb; ++i)
+		max = MAX(base[n + i], max);
+	for (size_t i = *nmemb; i < n; ++i)
+		base[n + i] = max;
+	for (size_t i = n; --i;)
+		base[i] = MIN(base[i << 1], base[(i << 1) + 1]);
+	*nmemb = n << 1;
+	return base;
+}
+
+void display(int *base, size_t nmemb, size_t node, size_t indent)
+{
+	if (node < 1 || node >= nmemb)
+		return;
+	display(base, nmemb, node << 1, indent + 1);
+	for (size_t i = 0; i++ < indent; putchar(9));
+	printf("%d", base[node]);
+	putchar(10);
+	display(base, nmemb, (node << 1) + 1, indent + 1);
+}
+
+size_t search(int value, int *base, size_t nmemb, size_t pos)
+{
+	if (pos < 1 || pos >= nmemb || base[pos] > value)
+		return 0;
+	if (base[pos] == value)
+		return pos;
+	size_t left = search(value, base, nmemb, pos << 1);
+	return left ? left : search(value, base, nmemb, (pos << 1) + 1);
+}
+
+void treeify(int *base, size_t nmemb, size_t node)
+{
+	if (node > 1 && node < nmemb && base[node >> 1] > base[node]) {
+		base[node >> 1] = base[node];
+		treeify(base, nmemb, node >> 1);
+	}
+}
+
+void insert(int value, size_t pos, int *base, size_t nmemb)
+{
+	if (pos >= nmemb >> 1 && pos < nmemb) {
+		base[pos] = value;
+		treeify(base, nmemb, pos);
+	}
+}
+
+void delete(size_t pos, int *base, size_t nmemb)
+{
+	if (pos > 1 && pos < nmemb) {
+		base[pos] = base[pos >> 1];
+		delete(pos << 1, base, nmemb);
+		delete((pos << 1) + 1, base, nmemb);
+	}
+}
+
+int main()
+{
+	size_t n;
+	puts("Array length:");
+	scanf("%zu", &n);
+
+	srand(time(NULL));
+	int *a = rand_array(n);
+	a = tree(a, &n);
+	display(a, n, 1, 0);
+
+	int x;
+	puts("Value to search for:");
+	scanf("%d", &x);
+	size_t i = search(x, a, n, 1);
+	if (i)
+		display(a, n, i, 0);
+	else
+		puts("Not found");
+
+	puts("Value to insert:");
+	scanf("%d", &x);
+	puts("Leaf index to insert to:");
+	scanf("%zu", &i);
+	insert(x, i, a, n);
+	display(a, n, 1, 0);
+
+	puts("Node to be deleted:");
+	scanf("%zu", &i);
+	delete(i, a, n);
+	display(a, n, 1, 0);
+
+	return 0;
+}
diff --git a/usth/ICT2.1/labwork/6/TT6.pdf b/usth/ICT2.1/labwork/6/TT6.pdf
new file mode 100644
index 0000000..d4d3bf5
--- /dev/null
+++ b/usth/ICT2.1/labwork/6/TT6.pdf
Binary files differ