Day11.java

import java.util.HashSet;
import java.util.Set;

public class Day11 {

	public static void main(String[] args) {

		String test1 = "abcdefgh";
		String expected1 = "abcdffaa";
		String test2 = "ghijklmn";
		String expected2 = "ghjaabcc";

		String result1 = generatePass(test1);
		String result2 = generatePass(test2);

		System.out.println("Test 1: " + test1 + " expected: " + expected1
				+ " generated: " + result1 + " ---> Test "
				+ (expected1.equals(result1) ? "passed" : "failed"));
		System.out.println("Test 2: " + test2 + " expected: " + expected2
				+ " generated: " + result2 + " ---> Test "
				+ (expected2.equals(result2) ? "passed" : "failed"));

		String password1 = "hxbxwxba";
		String password2 = generatePass(password1);

		System.out.println("Part 1: " + password1 + " ---> " + password2);
		System.out.println("Part 2: " + password2 + " ---> "
				+ generatePass(password2));

	}

	public static boolean threeStraightLetters(char[] pass) {
		for (int i = 0; i < pass.length - 2; i++) {
			if ((pass[i] == pass[i + 1] - 1)
					&& (pass[i + 1] == pass[i + 2] - 1)) {
				return true;
			}
		}
		return false;
	}

	public static boolean noForbiddenLetters(char[] pass) {
		for (char ch : pass) {
			if ((ch == 'i') || (ch == 'l') || (ch == 'o')) {
				return false;
			}
		}
		return true;
	}

	public static boolean doubleDifferentPair(char[] pass) {
		int count = 0;
		Set<Character> chars = new HashSet<>();
		for (int i = 0; i < pass.length - 1; i++) {
			if ((pass[i] == pass[i + 1])
					&& ((chars.isEmpty()) || (!chars.contains(pass[i])))) {
				count++;
				chars.add(pass[i]);
				if (count >= 2) {
					return true;
				}
			}
		}
		return false;
	}

	public static String generatePass(String password) {
		char[] pass = password.toCharArray();
		int passLen = pass.length - 1;
		while ((!(threeStraightLetters(pass) && noForbiddenLetters(pass) && doubleDifferentPair(pass)))
				|| (password.equals(String.valueOf(pass)))) {
			for (int i = passLen; i >= 0; i--) {
				pass[i] = (char) ((int) pass[i] + 1);
				if (!(pass[i] == (char) ((int) 'z') + 1)) {
					break;
				} else {
					pass[i] = 'a';
				}
			}
		}
		return String.valueOf(pass);
	}
}