蓝桥杯2023国赛--最大区间17152--[单调栈]

传送门 0最大区间 - 蓝桥云课

详见注解

const int N = 3e5 + 10;



int n;
LL stk[N],top;
LL a[N],l[N],r[N];
void solve()
{
	cin >> n;
	for (int i = 1;i <= n;i ++) cin >> a[i];
	
	//找左右第一个比a[i]小的位置
	
	for (int i = 1;i <= n;i ++)
	{
		while(top && a[stk[top]] >= a[i]) top --;
		if (top) l[i] = stk[top];
		else l[i] = 0;
		
		stk[++top] = i;
	}
	
	top = 0;
	for (int i = n;i >= 1;i --)
	{
		while(top && a[stk[top]] >= a[i]) top --;
		if (top) r[i] = stk[top];
		else r[i] = n + 1;
		
		stk[ ++top] = i;
	}
	
	// for (int i = 1;i <= n;i ++) cout << l[i] << " "; cout << endl;
	// for (int i = 1;i <= n;i ++) cout << r[i] << " "; cout << endl;
	
	LL ans = 0;
	for (int i = 1;i <= n;i ++)
		ans = max(ans,a[i] * (r[i] - l[i] - 1));区间长度-两端 == r - l + 1 - 2;

	cout << ans << endl;
}