Leetcode 226. Invert Binary Tree

Invert a binary tree.

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

to

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

使用递归的trival solution

 class Solution(object):
     def invertTree(self, root):
         """
         :type root: TreeNode
         :rtype: TreeNode
         """
         if not root:
             return

         root.left, root.right = root.right, root.left
         self.invertTree(root.right)
         self.invertTree(root.left)

         return root
         

非递归的话，需要一个queue辅助。

 class Solution(object):
     def invertTree(self, root):
         """
         :type root: TreeNode
         :rtype: TreeNode
         """
         if not root:
             return

         queue = [root]

         while queue:
             node = queue.pop(0)
             if node.left:
                 queue.append(node.left)
             if node.right:
                 queue.append(node.right)
             node.left, node.right = node.right, node.left

         return root