hdoj 1506 Largest Rectangle in a Histogram

DP 找出 a[i] 的左邊和右邊與自己連著的比自己大的數的長度 , 然後用這個長度乘以 a[i], 乘積最大的那個就是答案 .

#include<stdio.h>#include<string.h>#define LL long long#define N 100005int i,n,t;LL a[N],l[N],r[N],max;int main(){    while (scanf("%d",&n) &&  n)    {        for (i=1; i<=n; ++i) scanf("%I64d",&a[i]);        l[1]=1;        r[n]=n;        for (i=2; i<=n; ++i)        {            t=i;            while (t>1 && a[i]<=a[t-1]) t=l[t-1];            l[i]=t;        }        for (i=n-1; i>=1; --i)        {            t=i;            while (t<n && a[i]<=a[t+1]) t=r[t+1];            r[i]=t;        }        max=0;        for (i=1; i<=n; ++i)        {            if ((r[i]-l[i]+1)*a[i]>max) max=(r[i]-l[i]+1)*a[i];        }        printf("%I64d\n",max);    }    return 0;}