31.leetcode题目226： 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：递归调用

class Solution {public:    TreeNode* invertTree(TreeNode* root) {        if(root==NULL)        return root;        TreeNode* temp=root->left;        root->left=root->right;        root->right=temp;        root->left=invertTree(root->left);        root->right=invertTree(root->right);        return root;    }};

Invert a binary tree.

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

to

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