Largest Rectangle in a Histogram（ＨＤＵ１５０６）

Largest Rectangle in a Histogram　ＨＤＵ１５０６

一道ＤＰ题：

思路：http://blog.csdn.net/qiqijianglu/article/details/8556852

#include <stdio.h>
#include <iostream>
using namespace std;
int a[100005];
int l[100005],r[100005];
int main()
{
  int n,i,j;
  long long  maxx,sum;
  while(~scanf("%d",&n)&&n)
  {
    maxx=-1;
    for(i=1;i<=n;i++)
      scanf("%lld",&a[i]);
    l[1]=1;
    r[n]=n;
    for(i=1;i<=n;i++,l[i]=i)
        while(a[l[i]-1]>=a[i] && l[i]>1)
            l[i]=l[l[i]-1];
     for(i=n;i>=1;i--,r[i]=i)
        while(a[r[i]+1]>=a[i] && r[i]<n)
            r[i]=r[r[i]+1];
    for(i=1;i<=n;i++)
    {
        sum=(long long)a[i]*(r[i]-l[i]+1);
        if(sum>maxx)
            maxx=sum;
    }
    cout<<maxx<<endl;
  }
  return 0;
}