POJ 2796 Feel Good

原题链接：POJ 2796 Feel Good

题意简述：

　　求某段区间的最小值*这段区间所有元素之和的最大值；

代码如下：

#include<iostream>
#include<cstdio>
using namespace std;
const int N = 100010;
typedef long long ll;
ll a[N], st[N], sum[N];
int n, top = 0;
ll ans = -1, l, r;
int main(){
    scanf("%d", &n);
    for(int i = 1; i <= n; i++)    scanf("%d", &a[i]);
    for(int i = 1; i <= n; i++)    sum[i] = sum[i - 1] + a[i];        //前缀和预处理 
    a[n + 1] = -1;
    for(int i = 1; i <= n + 1; i++){
        
        while(top && a[st[top]] > a[i]){
            ll temp = (ll)a[st[top]] * (sum[i - 1] - sum[st[top - 1]]);    
        
            if(ans < temp){
                ans = temp;
                l = st[top - 1] + 1;
                r = i - 1;
                
            }
            --top;
        }
        ++top;
        st[top] = i;
    }
    printf("%lld
%lld %lld
", ans, l, r);
    return 0;
}