Isomorphic Strings

/*
 * Problem : Process two words.
 * Input   : Two words separated by a space.
 * Output  : true or false.
 * Approach: Two maps.
 * Time    : O(n)
 * Space   : O(1) for a fixed alphabet
 * Java    : 8 or newer.
 */
import java.util.Scanner;

public class Main {
    // This method solves the task. It receives the input and returns the answer.
    static boolean solve(String a, String b) {
        // Step 1: Words of different length cannot be isomorphic.
        if (a.length() != b.length()) {
            return false;
        }

        // Step 2: Keep two maps: a-letter to b-letter, and b-letter to a-letter. Both must stay consistent.
        java.util.Map<Character, Character> forward = new java.util.HashMap<>();
        java.util.Map<Character, Character> backward = new java.util.HashMap<>();

        for (int i = 0; i < a.length(); i++) {
            char x = a.charAt(i);
            char y = b.charAt(i);

            // Step 3: If a letter was mapped before to something else, the words are not isomorphic.
            if (forward.containsKey(x) && forward.get(x) != y) {
                return false;
            }
            if (backward.containsKey(y) && backward.get(y) != x) {
                return false;
            }
            forward.put(x, y);
            backward.put(y, x);
        }
        return true;
    }

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        String a = scanner.next();
        String b = scanner.next();
        System.out.println(solve(a, b));
    }
}