【Leetcode-easy-226】Invert Binary Tree

题目

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.

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思路

递归

和剑指offer 面试题19 二叉树的镜像基本一样。

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程序

/** * Definition for a binary tree node. * public class TreeNode { *     int val; *     TreeNode left; *     TreeNode right; *     TreeNode(int x) { val = x; } * } */class Solution {    public TreeNode invertTree(TreeNode root) {        mirrorTree(root);        return root;    }    private void mirrorTree(TreeNode root) {        if (root == null) return;        TreeNode tmp = root.left;        root.left = root.right;        root.right = tmp;        mirrorTree(root.left);        mirrorTree(root.right);    }}

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声明：题目来自Leetcode。