1840A - Cipher Shifer - CodeForces Solution

#include <bits/stdc++.h>
using namespace std;

#include <ext/pb_ds/assoc_container.hpp>
using namespace __gnu_pbds;

int main( ) {
ios_base::sync_with_stdio(false);
cin.tie(NULL);

// genius_koder
int t;
cin>>t;

while(t--) {
    int n;
    cin>>n;

    string s;
    cin>>s;

    string res="";
    int curr = 0;
    int prevLen = 0;
    while(curr < n) {
        res += s[curr];
        ++curr;
        while(s[curr]!=res.back()) {
            curr++;
        }
        ++curr;
    }    
    cout<<res<<endl;
}
return 0;
}