hdu 1506 Largest Rectangle in a Histogram ((dp求最大子矩阵))

# include <stdio.h>
# include <algorithm>
# include <iostream>
# include <math.h>
using namespace std;
__int64 a[100010],l[100010],r[100010];///l[i]左边连续大于等于a[i]的下标，r[i]右边连续大于等于a[i]的下标，所以对于a[i]的矩形面积为（l[i]-r[i]+1）*a[i];
int main()
{
__int64 maxn;
int i,n;
while(~scanf("%d",&n),n)
{
for(i=1;i<=n;i++)
{
scanf("%I64d",&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];
}
maxn=-1;
for(i=1;i<=n;i++)
{
if(a[i]*(r[i]-l[i]+1)>maxn)
maxn=a[i]*(r[i]-l[i]+1);
}
printf("%I64d\n",maxn);
}
return 0;
}