[C++知识库]你能回答这些问题吗（线段树模板）

AcWing245

#define ll long long int
#define tp t[p]
#define tl t[p << 1]
#define tr t[p << 1 | 1]
const int inf = 0x3f3f3f3f;
const int N = 5e5 + 3, M = N * 4;
int n, m;
int a[N];

struct node
{
	int l, r;
	int sum, lm, rm, date;
	node()//初始化
	{
		l = r = 0;
		sum = 0; 
		lm = rm = date = -inf;
	}

	node(int a, int b, int c, int d, int e, int f)//方便赋值
	{
		l = a; r = b; sum = c, lm = d, rm = e, date = f;
	}


}t[N * 4];

void seg(int p)
{
	tp.sum = tl.sum + tr.sum;
	tp.lm = max(tl.lm, tl.sum + tr.lm);
	tp.rm = max(tr.rm, tl.rm + tr.sum);
	tp.date = max({ tr.date, tl.date, tl.rm + tr.lm });
}

void build(int p, int l, int r)
{
	tp.l = l, tp.r = r;
	if (l == r) { tp.date = tp.lm = tp.rm = tp.sum = a[l]; return; }
	int mid = l + r >> 1;
	build(p << 1, l, mid);
	build(p << 1 | 1, mid + 1, r);
	seg(p);
}

void change(int p, int x, ll v)
{
	if (tp.l == tp.r) { tp.date = tp.lm = tp.rm = tp.sum = v; return; }
	int mid = tp.l + tp.r >> 1;
	if (x <= mid) change(p << 1, x, v);
	else change(p << 1 | 1, x, v);
	seg(p);
}

node ask(int p, int l, int r)
{
	if (l <= tp.l && r >= tp.r) return tp;
	int mid = tp.l + tp.r >> 1;

	node a, b, c;
	c = { l, r, 0, -inf, -inf, -inf };
	if (l <= mid) a = ask(p << 1, l, r);
	if (r > mid) b = ask(p << 1 | 1, l, r);

	c.sum = a.sum + b.sum;
	c.lm = max(a.lm, a.sum + b.lm);
	c.rm = max(a.rm + b.sum, b.rm);
	c.date = max({ a.date, b.date, a.rm + b.lm });

	return c;
}

int main()
{
	IOS;
	int n, m; cin >> n >> m;
	for (int i = 1; i <= n; i++) cin >> a[i];

	build(1, 1, n);
	int k, x, y;
	while (m--)
	{
		cin >> k >> x >> y;
		if (k == 1)
		{
			if (x > y) swap(x, y);
			cout << ask(1, x, y).date << endl;
		}
		else change(1, x, y);
	}


	return 0;
}

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