84.cpp

/**
 *    author:   vulkan
 *    created:  10.03.2020 06:02:17 PM
**/
#include <bits/stdc++.h>

using namespace std;

int largestRectangleArea(vector<int> &heights) {
    int n = heights.size();
    if (n == 0) {
        return 0;
    }

    vector<pair<int, int>> small(n);
    stack<int> st;
    for (int i = 0; i < n; ++i) {
        while (not st.empty() and heights[i] < heights[st.top()]) {
            small[st.top()].second = i;
            st.pop();
        }

        if (st.empty()) {
            small[i].first = -1;
        } else {
            small[i].first = st.top();
        }

        st.push(i);
    }

    while (not st.empty()) {
        small[st.top()].second = n;
        st.pop();
    }

    int max_area = INT_MIN;
    for (int i = 0; i < n; ++i) {
        max_area = max({
            max_area,
            (small[i].second - small[i].first - 1) * heights[i]
        });
    }

    return max_area;
}

int main(int argc, char const *argv[]) {
    int n;
    cin >> n;
    vector<int> heights(n);
    for (int i = 0; i < n; ++i) {
        cin >> heights[i];
    }

    cout << largestRectangleArea(heights);

    return 0;
}