secretmessage.cpp

#include <iostream>
#include <string>
#include <vector>
#include <cmath>

using namespace std;

string encode(string s, int size) {
    vector<vector<char>> v;
    v.resize(size, vector<char>(size));

    for(int i = 0; i < size; i++) {
        for(int j = 0; j < size; j++) {
            v[i][j] = s[(i*size)+j];
        }
    }

    string ret = "";

    for(int i = 0; i < size; i++) {
        for(int j = size-1; j >= 0; j--) {
            char temp = v[j][i];
            if(temp != '*') {
                ret += temp;
            }
        }
    }

    return ret;
}

int main() {
    int n;
    cin >> n;

    for(int i = 0; i < n; i++) {
        string s;
        cin >> s;

        int size = ceil(sqrt(s.length()));

        while(s.length() < pow(size, 2)) {
            s.push_back('*');
        }

        cout << encode(s, size) << endl;
    }
}