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;
    }
};