Codeforces 696 B

#include <bits/stdc++.h>
#define ll long long
#define ld long double
#define pb push_back
#define p_b pop_back
#define si stack<int>
#define sll stack<ll>
#define sc stack<char>
#define vi vector<int>
#define vll vector<ll>
#define mii map<int, int>
#define msi map<string, int>
#define mci map<char, int>
#define qc queue<char>
#define qi queue<int>
#define qll queue<ll>
using namespace std;

int main(){
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    int t;
    cin >> t;
    while(t--){
        int n;
        cin >> n;

        string s, t = "1";
        cin >> s;

        for(int i = 1; i < n; i++){
            if(s[i] == '0'){
                if(s[i-1] == '0'){
                    if(t[i-1] == '1'){
                        t += '0';
                    } else{
                        t += '1';
                    }
                } else{
                    if(t[i-1] == '0'){
                        t += '0';
                    } else{
                        t += '1';
                    }
                }
            } else{
                if(s[i-1] == '0'){
                    t += '1';
                } else{
                    if(t[i-1] == '1'){
                        t += '0';
                    } else{
                        t += '1';
                    }
                }
            }
        }

        cout << t << "\n";
    }
    return 0;
}