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 != NULL && q == NULL) return false;
        if (p->val != q->val) return false;
        return isSameTree(p->left,q->left) && isSameTree(p->right,q->right);
    }
};