closest pair of points in 2D plane

/*closest pair of points in 2D plane */

bool comp(const pii &a,const pii &b){
    return a.ss< b.ss;
}

pii v[MAX];

ll closest_pair(pii arr[],int N){
    // return square of closest pair of point

    ll best=1e18;
    set<pii> box;
    box.insert(arr[1]);


    int left=1;
    for(int i=2;i<=N;++i){
        while(left<i && arr[i].ss- arr[left].ss > sqrt(best)){
            box.erase(arr[left++]);
        }
        int cnt=0;
        for(auto it= box.lower_bound({arr[i].ff-sqrt(best),0}); it!=box.end() && arr[i].ff+sqrt(best) >= it->ff;it++){
            ll cy=arr[i].ff- it->ff;
            ll cx= arr[i].ss- it->ss;
            ll d= 1LL*cx*cx + 1LL*cy*cy;
            best=min(best,d);
        }
        box.insert(arr[i]);

    }
    return best;
}


int main()
{
    booster()
    ///read("input.txt");

    int n;
    cin>>n;

    for(int i = 1;i<=n;i++){
        cin>>v[i].ff;// ff => y cordinate
        v[i].ff += v[i-1].ff ;
        v[i].ss = i;
    }

    cout<<closest_pair(v,n);


    return 0;
}