Commit b5e7190

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+│   You are given the root of a binary tree. Invert the binary tree in
+│   place. That is, all left children should become right children, and all
+│   right children should become left children.
+│   Example:
+│    a
+│   / \
+│  b   c
+│ / \  /
+│d   e f
+│
+│   The inverted version of this tree is as follows:
+│  a
+│ / \
+│ c  b
+│ \  / \
+│  f e  d
+│
+│   Here is the function signature:
+│class Node:
+│  def __init__(self, value):
+│    self.left = None
+│    self.right = None
+│    self.value = value
+│  def preorder(self):
+│    print self.value,
+│    if self.left: self.left.preorder()
+│    if self.right: self.right.preorder()
+│def invert(node):
+│  # Fill this in.
+│root = Node('a')
+│root.left = Node('b')
+│root.right = Node('c')
+│root.left.left = Node('d')
+│root.left.right = Node('e')
+│root.right.left = Node('f')
+│root.preorder()
+│# a b d e c f
+│print "\n"
+│invert(root)
+│root.preorder()
+│# a c f b e d