leetcode 100. Same Tree

class Solution {
public:
    bool isSameTree(TreeNode* p, TreeNode* q) {
        if(p == NULL && q == NULL)
            return true;
        else 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);
    }
};