largest rectangle area in histogram optimized code leetcode

class Solution {
public:
    // Time Complexity:- O(N)
    // Space Complexity:- O(N)
    int largestRectangleArea(vector<int>& heights) {
        int n = heights.size();
        stack <int> index; // stack helps in storing increasing elements indices

        int max_area = 0;
        for(int i=0;i<heights.size();i++){
            while(!index.empty() and heights[i]<heights[index.top()]){
                int w = heights[index.top()];
                index.pop();

                int left = index.empty()?-1:index.top();
                int right = i;

                int l = right - left - 1;

                max_area = max(max_area,l*w);
            }
            index.push(i);
        }

        while(!index.empty()){
            int w = heights[index.top()];
            index.pop();

            int left = index.empty()?-1:index.top();
            int right = n;

            int l = right - left - 1;

            max_area = max(max_area,l*w);
        }

        return max_area;
    }
};