class Solution {public:    bool isSameTree(TreeNode *p, TreeNode *q)     {        if (!p) return !q;        if (!q) return !p;
        bool lflag = true;    
        if (p -> val == q -> val)        {            lflag = isSameTree(p -> left, q -> left);            return lflag && isSameTree(p -> right, q -> right);        }        else            return false;    }};