单调栈

https://www.acwing.com/problem/content/133/

求柱状图最大矩形面积

#include<bits/stdc++.h>
using namespace std;
long long  a[120000];
long long sta[12000],l[120000],r[120000];

int main()
{
    long long i,j,m,n,left,right,tail,ans;
    while(scanf("%lld",&n)!=EOF)
    {
        if(n==0)
            break;

        tail = -1;
        for(i = 1; i<=n; i++)
        {
            scanf("%lld",&a[i]);
        }
        tail = -1;
        a[0] = -1;
        sta[++tail] = 0;
        for(i = 1; i<=n; i++)
        {
            while(a[sta[tail]]>=a[i])
                tail--;
            l[i] = sta[tail]+1;
            sta[++tail] = i;
        }
        tail = -1;
        a[n+1] = -1;
        sta[++tail] = n+1;
        for(i = n; i>=1; i--)
        {
            while(a[sta[tail]]>=a[i])
                tail--;
            r[i] = sta[tail]-1;
            sta[++tail] = i;
        }
        ans = 0;
        for(i = 1; i<=n; i++)
        {
            ans = max(ans,a[i]*(r[i]-l[i]+1));
        }
        printf("%lld\n",ans);

    }

    return 0;
}