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+# Trees
+## Problem 1
+`graph-is-tree.cc` (C++17) take a natural numbers `n` and a `n`-by-`n` adjacent
+matrix from stdin and print to stdout either yes or no depending on whether the
+given graph is a tree or not, e.g.
+
+### Input
+    3
+    0 1 0
+    1 0 1
+    0 1 0
+
+### Output
+    yes
+
+## Problem 2
+`binary-search-tree.c` takes a natural number `n` and `n` integers from stdin
+and print to stdout a horizontal binary search tree formed (naïvely) from the
+given input, e.g.
+
+### Input
+    7
+    34 45 21 65 12 546 23
+
+### Output
+            12
+        21
+            23
+    34
+        45
+            65
+                546
+
+## Problem 3
+`dc.cc` takes from stdin a list of numbers and operator, each terminated by a
+semi-colon and print to stdout the evaluation of the given postfix arithmetic
+expression, e.g.
+
+### Input
+    6.9;4.20;+;2;^;6.9;4;-;3;/;+;
+
+### Output
+    124.177
+
+## Problem 4
+`st-dfs.cc` (C++17) takes a natural number `n` and an `n`-by-`n` adjacent
+matrix from stdin and print the edges on a spanning tree of the given graph to
+stdout, e.g.
+
+### Input
+    4
+    0 1 1 1
+    1 0 1 1
+    1 1 0 1
+    1 1 1 0
+
+### Output
+    2 3
+    0 3
+    1 2
+
+## Problem 5
+`sum-set.cc` takes a natural number `n` and a line of positive integers on one
+line from stdin and print numbers whose sum are `n`, separated by a newline, to
+stdout, e.g.
+
+### Input
+    7
+    1 2 3 4 5 6 7 8 9
+
+### Output
+    1 2 4
+    1 6
+    2 5
+    3 4
+    7