public static String encryption(String s) {
    s = s.replaceAll(" ", ""); 
    int col = (int) Math.ceil(Math.sqrt(s.length()));
    String encrypt = "";

    for (int i = 0; i < col; i++) {
        for (int j = 0; j < s.length(); j += col) {
            String str = s.substring(j);
            encrypt += (str.length() - 1 >= i) ? str.charAt(i) : "";
        }
        encrypt += " ";
    }
        
    return encrypt;
}