HDU 1506 Largest Rectangle in a Histogram

Problem Description
A histogram is a polygon composed of a sequence of rectangles aligned at a common base line. The rectangles have equal widths but may have different heights. For example, the figure on the left shows the histogram that consists of rectangles with the heights 2, 1, 4, 5, 1, 3, 3, measured in units where 1 is the width of the rectangles:
View Code

#include<stdio.h>
#include<string.h>
int a[100001];
int r[100001];
int l[100001];
int main()
{
int i,n;
__int64 max,temp;
while(scanf("%d",&n)&&n)
{
for(i=1;i<=n;i++)
{
scanf("%d",&a[i]);
l[i]=r[i]=i;
}
for(i=2;i<=n;i++)
{
while(l[i]>1&&a[l[i]-1]>=a[i])
l[i]=l[l[i]-1];
}
for(i=n-1;i>=1;i--)
{
while(r[i]<n&&a[r[i]+1]>=a[i])
r[i]=r[r[i]+1];
}
max=0;
for(i=1;i<=n;i++)
{
temp=(__int64)(r[i]-l[i]+1)*a[i];
if(max<temp)
max=temp;
}
printf("%I64d\n",max);
}
return 0;
}