/**
  * 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:
     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);
     }
 };