LeetCode 226----Invert Binary Tree

Invert a binary tree.

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

to

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

二叉树反转，采用递归的方式。

1. 输入结点为空时，返回为空；
2. 将右子树反转，left指向右子树；将左子树反转，将right指向左子树。

/** * 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;        TreeNode* p=root->left;        root->left=invertTree(root->right);        root->right=invertTree(p);        return root;    }};