POJ 2559 Largest Rectangle in a Histogram 单调栈

题目：

题意：

思路：

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <cmath>
using namespace std;

typedef long long ll;
const int N = 100010;
int arr
, st
, l
, r
;
int main()
{
int n;
while(scanf("%d", &n), n)
{
for(int i = 1; i <= n; i++) scanf("%d", &arr[i]);
int k = 0;
for(int i = 1; i <= n; i++)
{
while(k > 0 && arr[st[k-1]] >= arr[i]) k--;
if(k == 0) l[i] = 1;
else l[i] = st[k-1] + 1;
st[k++] = i;
}
k = 0;
for(int i = n; i >= 1; i--)
{
while(k > 0 && arr[st[k-1]] >= arr[i]) k--;
if(k == 0) r[i] = n;
else r[i] = st[k-1] - 1;
st[k++] = i;
}
ll res = -1;
for(int i = 1; i <= n; i++) res = max(res, (ll)arr[i] * (r[i] - l[i] + 1));
printf("%lld\n", res);
}
return 0;
}