Add solution for challenge #61

Author: Mauricio Klein

README.md

@@ -60,3 +60,4 @@
 - [x] [Challenge 58: Get all Values at a Certain Height in a Binary Tree](challenge-58/)
 - [x] [Challenge 59: Sort Colors](challenge-59/)
 - [x] [Challenge 60: Group anagrams](challenge-60/)
+- [x] [Challenge 61: Full Binary Tree](challenge-61/)

challenge-61/Makefile

@@ -0,0 +1,4 @@
+test:
+	python test_*.py
+
+.PHONY: test

challenge-61/README.md

@@ -0,0 +1,27 @@
+# Full Binary Tree
+
+This problem was asked by Google.
+
+## Description
+
+Given a binary tree, remove the nodes in which there is only 1 child, so that the binary tree is a full binary tree.
+
+So leaf nodes with no children should be kept, and nodes with 2 children should be kept as well.
+
+## Example
+
+```
+Given this tree:
+    1
+   / \ 
+  2   3
+ /   / \
+0   9   4
+
+We want a tree like:
+    1
+   / \ 
+  0   3
+     / \
+    9   4
+```

challenge-61/__init__.py

@@ -0,0 +1,40 @@
+from collections import deque
+
+class Node(object):
+  def __init__(self, value, left=None, right=None):
+    self.value = value
+    self.left = left
+    self.right = right
+
+  def __str__(self):
+    q = deque()
+    q.append(self)
+    result = ''
+    while len(q):
+      num = len(q)
+      while num > 0:
+        n = q.popleft()
+        result += str(n.value)
+        if n.left:
+          q.append(n.left)
+        if n.right:
+          q.append(n.right)
+        num = num - 1
+      if len(q):
+        result += "\n"
+
+    return result
+
+def full_binary_tree(node):
+  if not node:
+    return None
+
+  left  = full_binary_tree(node.left)
+  right = full_binary_tree(node.right)
+
+  if (left and right) or (not left and not right):
+    node.left  = left
+    node.right = right
+    return node
+  else:
+    return left or right

challenge-61/solver.py

@@ -0,0 +1,43 @@
+import unittest
+from solver import Node, full_binary_tree
+
+class TestSolver(unittest.TestCase):
+  def test_full_binary_tree(self):
+    #     1               1
+    #    / \             / \
+    #   2   3    ---->  0   3
+    #  /   / \             / \
+    # 0   9   4           9   4
+    root = Node(1, Node(2, Node(0)), Node(3, Node(9), Node(4)))
+    expected_str_output = "1\n03\n94"
+
+    self.assertEqual(str(full_binary_tree(root)), expected_str_output)
+
+    #     1                1
+    #    / \              / \
+    #   3   2    ---->   3   4
+    #  / \   \          / \
+    # 0   9   4        0   9
+    root = Node(1, Node(3, Node(0), Node(9)), Node(2, right=Node(4)))
+    expected_str_output = "1\n34\n09"
+
+    self.assertEqual(str(full_binary_tree(root)), expected_str_output)
+
+    #   1         3
+    #  /   ---->
+    # 3
+    root = Node(1, Node(3))
+    expected_str_output = "3"
+
+    self.assertEqual(str(full_binary_tree(root)), expected_str_output)
+
+    #   1           3
+    #    \   ---->
+    #     3
+    root = Node(1, right=Node(3))
+    expected_str_output = "3"
+
+    self.assertEqual(str(full_binary_tree(root)), expected_str_output)
+
+if __name__ == "__main__":
+    unittest.main()