HISTOGRA - 最大矩形面积（单调栈）

#include<bits/stdc++.h>
using namespace std;
#define x first
#define y second
typedef pair<int,int> PII;
typedef long long ll;
typedef unsigned long long ull;
typedef unsigned int uint;
typedef vector<string> VS;
typedef vector<int> VI;
typedef vector<vector<int>> VVI;
vector<int> vx;
inline int mp(int x) {return upper_bound(vx.begin(),vx.end(),x)-vx.begin();}
inline int log_2(int x) {return 31-__builtin_clz(x);}
inline int popcount(int x) {return __builtin_popcount(x);}
inline int lowbit(int x) {return x&-x;}
const int N = 1e5+10;
int stk[N],a[N],w[N];
void solve()
{
	//对于一个单调递增序列最大矩形面积应该是枚举左端点乘以长度
	int n;
	while(cin>>n,n)
	{
		int tt = 0;
		ll maxn = 0;
		for(int i=1;i<=n;++i) cin>>a[i];
		a[n+1] = 0;
		stk[0] = 0;
		//需要用width来维护累计矩形宽度
		//i枚举到n+1为了弹出最后一个矩形注意要把a[n+1]赋值
		for(int i=1;i<=n+1;++i)
		{
			if(a[i]>stk[tt]) stk[++tt] = a[i], w[tt] = 1;
			else 
			{
				int width = 0;
				while(tt&&a[i]<stk[tt]) 
				width += w[tt], maxn = max(maxn,(ll)width*stk[tt--]);
				stk[++tt] = a[i], w[tt] = width + 1;
			}
		}
		cout<<maxn<<'\n';
	}
}
int main()
{
	ios::sync_with_stdio(false);
	cin.tie(0);
	int T = 1;
	//cin>>T;
	while(T--)
	{
		solve();
	}
}