226. Invert Binary Tree

1.描述

Invert a binary tree.

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

to

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

2.分析

3.代码

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    TreeNode* invertTree(TreeNode* root) {
        if (root == NULL)
            return NULL;
        if (root->left != NULL) 
            invertTree(root->left);
        if (root->right != NULL) {
            invertTree(root->right);
        }
        TreeNode* tmp = root->left;
        root->left = root->right;
        root->right = tmp;
        return root;
    }
};