class Solution {
public:int largestRectangleArea(vector<int>& heights) {stack<int>st;heights.insert(heights.begin(),0);heights.push_back(0);st.push(0);int res=0;for(int i=1;i<heights.size();i++){while(heights[i]<heights[st.top()]){int mid=st.top();st.pop();int w=i-st.top()-1;int h=heights[mid];res=max(h*w,res);}st.push(i);}
return res;}
};