Decrypt

import java.io.*;
import java.util.HashMap;
import java.util.Map;

/**
 * Created by migho on 6.9.2016.
 */
public class Main {

    //nopqrstuvwxyzabcdefghijklmn
    //tbbqvqrn

    public static void main(String[] argv) {
        IO io = new IO();

        // characters
        char[] f = io.next().toCharArray();

        //rounds
        int k = io.nextInt();

        //encrypted message
        char[] encryptedString = io.next().toCharArray();

        char[] alphabet = "abcdefghijklmnopqrstuvwxyz".toCharArray();

        Map<Character, Character> data = new HashMap<>();
        for(int i = 0; i < k; i++) {
            for (int offset = 0; offset < encryptedString.length; offset++) {
                char c = encryptedString[offset];
                if (data.containsKey(c)) {
                    encryptedString[offset] = data.get(c);
                    continue;
                }
                int pos = 0;
                for (char x : f) {
                    if (x == c) {
                        break;
                    }
                    pos++;
                }
                //int pos = Arrays.binarySearch(f, c);
                if (pos > 25) {
                    System.out.println("impossible");
                    System.exit(0);
                }
                data.put(encryptedString[offset], alphabet[pos]);
                encryptedString[offset] = alphabet[pos];
            }
        }

        System.out.println(new String(encryptedString));
    }

}

Test 1

Verdict: ACCEPTED

Test 2

Verdict: WRONG ANSWER

Test 3

Verdict: TIME LIMIT EXCEEDED

Test 4

Verdict: ACCEPTED

Test 5

Verdict: ACCEPTED

Test 6

Verdict: ACCEPTED

Test 7

Verdict: TIME LIMIT EXCEEDED

Test 8

Verdict: WRONG ANSWER

Test 9

Verdict: TIME LIMIT EXCEEDED

Test 10

Verdict: ACCEPTED

Test 11

Verdict: ACCEPTED

Test 12

Verdict: ACCEPTED

Test 13

Verdict: TIME LIMIT EXCEEDED

Test 14

Verdict: ACCEPTED

Test 15

Verdict: TIME LIMIT EXCEEDED

Test 16

Verdict: ACCEPTED

Test 17

Verdict: ACCEPTED

Test 18

Verdict: ACCEPTED

Test 19

Verdict: ACCEPTED

Test 20

Verdict: ACCEPTED

Test 21

Verdict: TIME LIMIT EXCEEDED

Test 22

Verdict: ACCEPTED

Test 23

Verdict: ACCEPTED

Test 24

Verdict: ACCEPTED

Test 25

Verdict: ACCEPTED

Test 26

Verdict: WRONG ANSWER

Test 27

Verdict: TIME LIMIT EXCEEDED

Test 28

Verdict: ACCEPTED

Test 29

Verdict: ACCEPTED

Test 30

Verdict: ACCEPTED