Largest Rectangle in Histogram

Given n non-negative integers representing the histogram's bar height where the width of each bar is 1, find the area of largest rectangle in the histogram.

Above is a histogram where width of each bar is 1, given height = [2,1,5,6,2,3].

 

The largest rectangle is shown in the shaded area, which has area = 10 unit.

 

For example,
Given heights = [2,1,5,6,2,3],
return 10.

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