leetcode 226. Invert Binary Tree

/** * 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:    void swap1(TreeNode*root){        if(root == NULL) return;        swap(root->left,root->right);        swap1(root->left);        swap1(root->right);    }    TreeNode* invertTree(TreeNode* root) {        swap1(root);        return root;    }};