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[];
 int l[],r[];
 int main()
 {
   int n,i,j;
   long long  maxx,sum;
   while(~scanf("%d",&n)&&n)
   {
     maxx=-;
     for(i=;i<=n;i++)
       scanf("%lld",&a[i]);
     l[]=;
     r[n]=n;
     for(i=;i<=n;i++,l[i]=i)
         while(a[l[i]-]>=a[i] && l[i]>)
             l[i]=l[l[i]-];
      for(i=n;i>=;i--,r[i]=i)
         while(a[r[i]+]>=a[i] && r[i]<n)
             r[i]=r[r[i]+];
     for(i=;i<=n;i++)
     {
         sum=(long long)a[i]*(r[i]-l[i]+);
         if(sum>maxx)
             maxx=sum;
     }
     cout<<maxx<<endl;
   }
   return ;
 }