POJ2559 (monotonous stack entry)

 

POJ2559

 

#include<cstdio>
#include<algorithm>
using namespace std;
#define ll long long
const int maxn=1e5+10;
int a[maxn];
int w[maxn];
int s[maxn];
int p=0;
int main()
{
    int n;
    while(scanf("%d",&n)&&n)
    {
        for(int i=1; i<=n; i++)
            scanf("%d",&a[i]);
        p=0;
        a[n+1]=0;
        ll ans=0;
        for(int i=1; i<=n+1; i++)
        {
            if(a[i]>=s[p])
            {
                s[++p]=a[i];
                w[p]=1;
            }
            else
            {
                int width=0;
                while(a[i]<s[p])
                {
                    width+=w[p];
                    ans=max(ans,(ll)width*s[p]);
                    p--;
                }
                s[++p]=a[i];
                w[p]=width+1;
            }
        }
        printf("%lld\n",ans);
    }
}