[leetcode]Largest Rectangle in Histogram

class Solution {public:    int largestRectangleArea(vector<int> &height) {        // Start typing your C/C++ solution below        // DO NOT write int main() function        if(height.empty()) return 0;                int N = height.size();        vector<int> left(N, 0);        vector<int> right(N, 0);                stack<int> s1;        s1.push(0);                for(int i = 1; i < N; i++){            if(height[i] > height[s1.top()]){                left[i] = 0;            }else{                while(!s1.empty() && height[i] <= height[s1.top()]){                    s1.pop();                }                if(s1.empty()){                    left[i] = i;                }else{                    left[i] = i-s1.top()-1;                }            }            s1.push(i);        }                stack<int> s2;        s2.push(N-1);                for(int i = N-2; i >= 0; i--){            if(height[i] > height[s2.top()]){                right[i] = 0;            }else{                while(!s2.empty() && height[i] <= height[s2.top()]){                    s2.pop();                }                if(s2.empty()){                    right[i] = N-i-1;                }else{                    right[i] = s2.top()-i-1;                }            }            s2.push(i);        }                for(int i = 0; i < N; i++){            left[i] =(left[i] + right[i] + 1) * height[i];        }        return *max_element(left.begin(), left.end());            }};