ZOJ-1985

求最大矩形面积，首先，O(n^2)的暴力算法肯定是超时的，不用想了。。必须改进，自己想了想没思路，然后搜了一下，看到求是大肥羊的那篇，思路就是求每个点左右两边比当它高度高的最长下标，类似DP的思想，后面的点可以利用前面求过的结果跳跃前进，非常巧妙，膜拜大牛。。

#include<stdio.h>

int main()
{
	int n, a[100000], left[100000], right[100000];
	while (scanf("%d", &n), n)
	{
		int i;
		for (i = 0; i < n; i++)
		{
			scanf("%d", &a[i]);
			left[i] = i;
			right[i] = i;
		}
		int temp;
		for (i = 0; i < n; i++)
		{
			temp = i;
			while (temp - 1 >= 0 && a[temp - 1] >= a[i])
				temp = left[temp - 1];
			left[i] = temp;
		}
		for (i = n - 1; i >= 0; i--)
		{
			temp = i;
			while (temp + 1 < n && a[temp + 1] >= a[i])
				temp = right[temp + 1];
			right[i] = temp;
		}
		long long max = -1, res;
		for (i = 0; i < n; i++)
		{
			res = (long long) a[i] * (long long) (right[i] - left[i] + 1);
			if (res > max)
				max = res;
		}
		printf("%lld\n", max);
	}
	return 0;
}