public boolean isSameTree(TreeNode p, TreeNode q) {
		if (p == null && q != null || p != null && q == null)
			return false;
		if (p == null && q == null)
			return true;
		if (p.val == q.val)
			return isSameTree(p.left, q.left) && isSameTree(p.right, q.right);
		else
			return false;
	}