AdventOfCode2025/src/Day01.java

package src;

import java.io.FileReader;
import java.util.Scanner;

public class Day01 {
    public static void main(String[] args) {
        part1();
        part2();
    }

    private static void part1() {
        try (Scanner scanner = new Scanner(new FileReader("resources/inputs/01/input"))) {
            int dial = 50;
            int password = 0;
            while (scanner.hasNextLine()) {
                String instruction = scanner.nextLine();
                int change = Integer.parseInt(instruction.substring(1));
                int step = switch (instruction.charAt(0)) {
                    case 'L' -> -1;
                    case 'R' -> 1;
                    default -> 0; // impossible
                };
                dial = (dial + change * step) % 100;
                if (dial == 0) {
                    password += 1;
                }
            }
            System.out.println(password);
        } catch (Exception e) {
            System.out.println(e.getMessage());
        }
    }

    // this is the inefficient way to do it, but it's also accurate!
    private static void part2() {
        try (Scanner scanner = new Scanner(new FileReader("resources/inputs/01/input"))) {
            int dial = 50;
            int password = 0;
            while (scanner.hasNextLine()) {
                String instruction = scanner.nextLine();
                int change = Integer.parseInt(instruction.substring(1));
                int step = switch (instruction.charAt(0)) {
                    case 'L' -> -1;
                    case 'R' -> 1;
                    default -> 0; // impossible
                };
                for (int i = 0; i < change; i++) {
                    dial = (dial + step) % 100;
                    if (dial == 0) {
                        password += 1;
                    }
                }
            }
            System.out.println(password);
        } catch (Exception e) {
            System.out.println(e.getMessage());
        }
    }
}