/** * Definition for binary tree * struct TreeNode { *     int val; *     TreeNode *left; *     TreeNode *right; *     TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */class Solution {public:    bool isSameTree(TreeNode *p, TreeNode *q) {        if (p == NULL && q == NULL) {            return true;        }        if (p == NULL || q == NULL) {            return false;        }        if (p->val != q->val) {            return false;        }        return isSameTree(p->left, q->left) && isSameTree(p->right, q->right);    }};