void rev(int x, int y){
	int p, q, r;
	split(x - 1, root, p, q);
	split(y, q, q, r);
	tree[q].tag ^= 1;
	root = merge(merge(p, q), r);
}

void rev(int x, int y){
	int p, q, r;
	split(y, root, q, r);
	split(x - 1, q, p, q);
	tree[q].tag ^= 1;
	root = merge(merge(p, q), r);
}

为何上方代码错误，下方正确？