1 files changed, 79 insertions, 0 deletions
diff --git a/daily/287easy/kaprekar.c b/daily/287easy/kaprekar.c
new file mode 100644
index 0000000..3121d88
--- /dev/null
+++ b/daily/287easy/kaprekar.c
@@ -0,0 +1,79 @@
+#include <stdio.h>
+
+char a[4];
+
+char largest_digit(short n) 
+{
+	char m = n / 1000;
+
+	if (m < n % 1000 / 100)
+		m = n % 1000 / 100;
+
+	if (m < n % 100 / 10)
+		m = n % 100 / 10;
+
+	return (m < n % 10) ? n % 10 : m;
+}
+
+void sort_digits(short n)
+{
+	char i, j;
+
+	a[0] = n / 1000;
+	a[1] = n % 1000 / 100;
+	a[2] = n % 100 / 10;
+	a[3] = n % 10;
+
+	for (i = 0; i < 3; i++)
+		for (j = i + 1; j < 4; j++)
+			if (a[i] < a[j]) {
+				a[i] += a[j];
+				a[j] = a[i] - a[j];
+				a[i] -= a[j];
+			}
+}
+
+short desc_digits(short n)
+{
+	sort_digits(n);
+
+	return a[0] * 1000 + a[1] * 100 + a[2] * 10 + a[3];
+}
+
+short asc_digits(short n)
+{
+	sort_digits(n);
+
+	return a[3] * 1000 + a[2] * 100 + a[1] * 10 + a[0];
+}
+
+unsigned long long kaprekar(short n)
+{
+	char i;
+
+	for (i = 0; n ^ 6174; i++)
+		n = desc_digits(n) - asc_digits(n);
+
+	return i;
+}
+
+int main()
+{
+	printf("largest_digit(1234) -> %hhd\n", largest_digit(1234));
+	printf("largest_digit(3253) -> %hhd\n", largest_digit(3253));
+	printf("largest_digit(9800) -> %hhd\n", largest_digit(9800));
+	printf("largest_digit(3333) -> %hhd\n", largest_digit(3333));
+	printf("largest_digit(120) -> %hhd\n\n", largest_digit(120));
+
+	printf("desc_digits(1234) -> %hd\n", desc_digits(1234));
+	printf("desc_digits(3253) -> %hd\n", desc_digits(3253));
+	printf("desc_digits(9800) -> %hd\n", desc_digits(9800));
+	printf("desc_digits(3333) -> %hd\n", desc_digits(3333));
+	printf("desc_digits(120) -> %hd\n\n", desc_digits(120));
+
+	printf("kaprekar(6589) -> %lld\n", kaprekar(6589));
+	printf("kaprekar(5455) -> %lld\n", kaprekar(5455));
+	printf("kaprekar(6174) -> %lld\n", kaprekar(6174));
+
+	return 0;
+}