Same Tree [LeetCode]

Problem Description: http://oj.leetcode.com/problems/same-tree/

 class Solution {
 public:
     bool isSameTree(TreeNode *p, TreeNode *q) {
         // Note: The Solution object is instantiated only once and is reused by each test case.
         if(p == NULL && q == NULL)
             return true;
         if(p == NULL && q != NULL ||
             (p != NULL && q == NULL))
             return false;
         if(p->val != q->val)
             return false;
         return isSameTree(p->left, q->left) && isSameTree(p->right, q->right);
     }
 };