Ada Byron Fase Local UPM - Problema 865 - Sustitution Cipher

Main.java

// https://www.geeksforgeeks.org/fast-io-in-java-in-competitive-programming/

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.Scanner;
import java.util.StringTokenizer;

import java.util.HashMap;

// Imports solo para leer decentemente.
// Por algo amamos Java para aprender a programar (no).


class Main {

    static class FastReader {
        BufferedReader br;
        StringTokenizer st;

        public FastReader() {
            br = new BufferedReader(new InputStreamReader(System.in));
        }

        String next(){
            while (st == null || !st.hasMoreElements()){
                try {
                    st = new StringTokenizer(br.readLine());
                } catch (IOException e) {
                    System.out.println("Error " + e.getMessage());
                }
            }
            return st.nextToken();
        }

        int nextInt(){
            return Integer.parseInt(next());
        }

        long nextLong(){
            return Long.parseLong(next());
        }

        double nextDouble(){
            return Double.parseDouble(next());
        }

        String nextLine(){
            String str = "";
            try {
                str = br.readLine();
            }
            catch (IOException e) {
                return null;
            }
            return str;
        }
    }


    public static void main (String [] args) { 

        FastReader fr = new FastReader();

        int n = fr.nextInt();
        // System.out.println("Número de casos: " + n);
                    
        fr.nextLine(); // Empty line

        for (int i = 0; i<n; i++){ // For cases

            // System.out.println("Caso " + i);
            if (i > 0)
                System.out.println("");

            String alfa = fr.nextLine();  // Se lee el alfabeto
            String sust = fr.nextLine(); // Se lee la sustitución

            System.out.println(sust);
            System.out.println(alfa);

            int len = alfa.length();           
            // System.out.println("Len: " + len);

            
            HashMap<Character, Character> cipher = new HashMap<Character, Character>(len);  // Estructura para el cambio (K->V)

            for (int j = 0; j<len; j++){
                // System.out.println("J: " + j + " Alfa: " + alfa.charAt(j) + " Sust: " + sust.charAt(j));
                cipher.put((Character) alfa.charAt(j), (Character) sust.charAt(j));
            }


            // System.out.println("HashMap size: " + cipher.size());
            // System.out.println("HashMap keys: " + cipher.get('c'));
            
            String line = fr.nextLine();
            
            while (line != null && !line.equals("")){

                for (Character c : line.toCharArray())
                    System.out.print(cipher.getOrDefault(c, c));

                System.out.println("");

                line = fr.nextLine();
                // System.out.println("Linea: " + line);
            }
        }
    }    
}