51Nod 1102 面积最大的矩形

#include <iostream>
#include <algorithm>
#include <stack>

using namespace std;
const int maxn = 50000 + 5;
long long a[maxn];
long long l[maxn], r[maxn];

int main(){
    ios::sync_with_stdio(false);
    int n;
    cin >> n;
    for (int i = 1; i <= n; i++){
        cin >> a[i];
        l[i] = r[i] = i;
    }
    for (int i = 1; i <= n; i++){
        while (a[l[i]-1] >= a[i]){
            l[i] = l[l[i] - 1];
        }
    }

    for (int i = n; i >= 1; i--){
        while (a[i] <= a[r[i] + 1]){
            r[i] = r[r[i] + 1];
        }
    }

    long long sum = -1;
    for (int i = 1; i <= n; i++){
        if (sum < a[i] * (r[i] - l[i] + 1))
            sum = a[i] * (r[i] - l[i] + 1);
    }
    cout << sum << endl;
    system("pause");
    return 0;
}