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); 
    }
};