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

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# 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;}

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