84. Largest Rectangle in Histogram

class Solution {
public:
    int largestRectangleArea(vector<int>& h) {
        stack<int> s;
        int res = 0;
        h.push_back(0);
        for (int i = 0; i < h.size(); i++) {
            while (!s.empty() && h[i] < h[s.top()]) {
                int cur = s.top();
                s.pop();
                int left = s.empty() ? -1 : s.top();
                res = max(res, (i - left - 1) * h[cur]);
            }
            s.push(i);
        }
        return res;
    }
};