Invert Binary Tree

题目：

Invert a binary tree.

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

to

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

分析：分析左右子树情况，利用递归

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) {               TreeNode *temp;        if(root!=NULL)        {            if(root->left==NULL&&root->right==NULL)            {                return root;            }            else if(root->left!=NULL&&root->right==NULL)            {                root->right=invertTree(root->left);                root->left=NULL;                            }            else if(root->left==NULL&&root->right!=NULL)            {                root->left=invertTree(root->right);                root->right=NULL;            }            else            {                temp=root->right;                root->right=invertTree(root->left);                root->left=invertTree(temp);                //res->val=root->val;            }        }        return root;    }};