226.py

'''
	Invert a binary tree.

	Example:

	Input:

	     4
	   /   \
	  2     7
	 / \   / \
	1   3 6   9

	Output:

	     4
	   /   \
	  7     2
	 / \   / \
	9   6 3   1
'''

# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution(object):
    def invertTree(self, root):
        """
        :type root: TreeNode
        :rtype: TreeNode
        """

        if not root:
        	return

        leftTree = self.invertTree(root.left)
        rightTree = self.invertTree(root.right)
        root.left = rightTree
        root.right = leftTree
        return root


# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution(object):
    def invertTree(self, root):
        """
        :type root: TreeNode
        :rtype: TreeNode
        """
        if not root:
        	return None
        
        queue = [root]
        while queue:
        	node = queue.pop(0)
        	node.left, node.right = node.right, node.left
        	if node.left:
        		queue.append(node.left)
        	if node.right:
        		queue.append(node.right)

        return root