argest Rectangle in Histogram

#pragma GCC target("avx2")
#pragma GCC optimize("O3")

#include<bits/stdc++.h>

using namespace std;
typedef long long int ll;
//#define isvowel(a) (a == 'a' || a == 'e' || a == 'i' || a == 'o' || a == 'u')
#define pb push_back
#define mp make_pair
#define fi first
#define se second
#define gcd __gcd
#define getl(s) getline(cin, s);
#define setpre(x) fixed << setprecision(x)
#define mset(a) memset(a, 0, sizeof(a))
#define endl '\n'
const int N=200050,M=1000000007;
const ll INF=1e18+7;
class Solution {
public:
    int largestRectangleArea(vector<int>heights) {
        stack<int>sta_pos,sta_h;
        int n=heights.size(),pos,val,maxis=0,inher;
        for(int i=0;i<n;++i){
            if(sta_pos.empty()){
                sta_pos.push(i);
                sta_h.push(heights[i]);
            }
            else{
                pos=sta_pos.top();
                val=sta_h.top();
                if(heights[i]==val) continue;
                if(heights[i]>val){
                    sta_pos.push(i);
                    sta_h.push(heights[i]);
                }
                else{
                    while(!sta_pos.empty()){
                        pos=sta_pos.top();
                        val=sta_h.top();
                        if(heights[i]<=val){
                            inher=pos;
                            maxis=max(maxis,(i-pos)*val);
                            sta_h.pop(); sta_pos.pop();
                        }
                        else break;
                    }
                    if(heights[i]==0) continue;
                    sta_pos.push(inher);
                    sta_h.push(heights[i]);
                }
            }
        }
        while(!sta_pos.empty()){
            pos=sta_pos.top();
            val=sta_h.top();
            maxis=max(maxis,(n-pos)*val);
            sta_pos.pop(); sta_h.pop();
        }
        return maxis;
    }
};
int main(){
    ios_base::sync_with_stdio(NULL); cin.tie(nullptr); cout.tie(nullptr);
//    freopen("RECT.inp","r",stdin);
//    freopen("RECT.out","w",stdout);
    int n,a;
    vector<int>v;
    cin>>n;
    for(int i=0;i<n;++i){
        cin>>a;
        v.push_back(a);
    }
    Solution A;
    cout<<A.largestRectangleArea(v);
    return 0;
}
/*
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INPUT:                            |
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6
2 1 5 6 2 3
------------------------------    |
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OUTPUT:                           |
------------------------------    |

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*/