LeetCode 226. Invert Binary Tree

Invert a binary tree.

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

to

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

这道题和判断树的对称性是一样的

递归翻转左右子树。

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