1932E - Final Countdown - CodeForces Solution

#include <iostream>
#include <string>
#include <vector>
#include <sstream>
#include <map>
#include <cmath>
#include <algorithm>
#include <queue>
#include <set>
#include <numeric>

using namespace std;
using ll = long long;

#define all(a) a.begin(), a.end()
#define repl(i, a, b) for (ll i = a; i < (b); ++i)
#define rep(i, b) for (ll i = 0; i < (b); ++i)

void solve() {
    ll n;
    cin >> n;
    string s;
    cin >> s;
    ll count = 0;
    vector<int> a(n,0);
    rep(i,n){
        count+=s[i]-'0';
        a[i] = count;
    }
    vector<int> x(2*n,0);
    rep(i,n){
        stringstream ss;
        ss << a[n-1-i];
        string str = ss.str();
        rep(j,str.size()){
            x[x.size()-1-i-j]+=str[str.size()-1-j]-'0';
            if(x[x.size()-1-i-j]>=10){
                x[x.size()-i-j-2]++;
                x[x.size()-1-i-j]-=10;
            }
        }

    }
    bool first = true;
    rep(i,2*n){
        if(first&&x[i] == 0) continue;
        first = false;
        cout << x[i];
    }
    cout << endl;
}

int main(){

    ios::sync_with_stdio(false);
    cin.tie(0);

    ll t = 1;
    cin >> t;
    while (t--) {
        solve();
    }
    
}