leetCode#226. Invert Binary Tree

Description

Invert a binary tree.
     4
   /   \
  2     7
 / \   / \
1   3 6   9
to
     4
   /   \
  7     2
 / \   / \
9   6 3   1

Trivia:
This problem was inspired by this original tweet by Max Howell:

Google: 90% of our engineers use the software you wrote (Homebrew), but you can’t invert a binary tree on a whiteboard so fuck off.

Code

# 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 root == None:
            return root
        root.left, root.right = root.right, root.left
        self.invertTree(root.left)
        self.invertTree(root.right)
        return root

Conclusion

该题比较简单，大家的思路也都基本一致。该题还有另一种解法，就是用队列，将需要invert的节点放进队列中，一个一个的替换，然后再将替换的节点的子节点放进去。这样的好处是解决了节点左右子节点互换的时候，子节点太大，导致中间缓存的temp开销太大，超出内存限制。某种情况下，是该思考的情形。