UVa - 11716 - Digital Fortress

#include <iostream>
#include <cstdio>
#include <string>
#include <cstring>
#include <cmath>
#include <vector>
using namespace std;

int main(){
    int t, limit, flag, i;
    string ans, code;
    cin >> t;
    getchar();
    while(t--){
        getline(cin, code);
        int l = code.size();limit = sqrt(l);flag = 0;
        for(i = 1; i <= limit; i++)
            if(i*i == l){flag = 1;break;}
        if(flag == 1){
            for(int j = 0; j < i; j++)
                for(int k = j; k < l; k += i)
                    ans.push_back(code[k]);
            cout << ans << endl;
        }
        else puts("INVALID");ans.clear();
    }

    return 0;
}