hdu1506 dp

题意:
  给你一个图形,让你找到最大的长方形.


思路:

     dp,开两个数组L[i],R[i],记录当前的这个点,左边连续大于等于他,和右边连续大于等于他的下标,O(n)的时间处理完这两个数组,然后枚举每一个点,如果以当前的点为长方形的高那么 now = (R[i] - L[i] + 1) * H[i],更新最大就行了...

#include<stdio.h>


#define N 100000 + 100

__int64  L[N] ,R[N];
__int64 H[N];

int main ()
{
   int n ,i;
   while(~scanf("%d" ,&n) && n)
   {
      for(i = 1 ;i <= n ;i ++)
      scanf("%I64d" ,&H[i]);
      L[1] = 1 ,R[n] = n;
      for(i = 2 ;i <= n ;i ++)
      {
         int k = i;
         while(k > 1 && H[i] <= H[k-1]) k = L[k-1];
         L[i] = k;
      }
      for(i = n - 1 ;i >= 1 ;i --)
      {
         int k = i;
         while(k < n && H[i] <= H[k+1]) k = R[k+1];
         R[i] = k;
      }
      __int64 max = 0;
      for(i = 1 ;i <= n ;i ++)
      {
         __int64 now = (R[i] - L[i] + 1) * H[i];
         if(max < now) max = now;
      }
      printf("%I64d\n" ,max);
   }
   return 0;
}