226. Invert Binary Tree

Problem Statement

Invert a binary tree.

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

to

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

Thinking

交换二叉树左右子树，主要还是注意递归结束条件。

Solution

/** * 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) {        TreeNode tmp;        if(root != null){            tmp = root.left;            root.left = root.right;            root.right = tmp;        }        else            return null;        invertTree(root.left);        invertTree(root.right);        return root;    }}