[LeetCode] Symmetric Tree

class Solution {public:    bool isSymmetric(TreeNode *root) {        if(root == NULL)            return true;        return check(root -> left,root -> right);    }    bool check(TreeNode * left,TreeNode *right){        if(left == NULL && right == NULL)            return true;        if(left == NULL || right == NULL)            return false;        return (left -> val == right -> val) && check(left -> right,right -> left)        && check(left -> left,right -> right);    }};