Advent of Code 2023 Day 1

package adventofcode2023day01;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.regex.Pattern;

public class Main {

  public static void main(String[] args) {
    System.out.println("Part 1: " + new Part1().result(Main.class.getResourceAsStream("/input.txt")));
    System.out.println("Part 2: " + new Part2().result(Main.class.getResourceAsStream("/input.txt")));
  }

  static class Part1 extends AoC2023Day1Processor {

    @Override
    protected int firstDigit(String line) {
      for (int i = 0; i < line.length(); ++i) {
        var character = line.charAt(i);
        if (character >= '0' && character <= '9') {
          return character - '0';
        }
      }
      return 0;
    }

    @Override
    protected int lastDigit(String line) {
      for (int i = line.length() - 1; i >= 0; --i) {
        var character = line.charAt(i);
        if (character >= '0' && character <= '9') {
          return character - '0';
        }
      }
      return 0;
    }

  }

  static class Part2 extends AoC2023Day1Processor {

    private static final String DIGIT_PATTERN_STRING = "(zero|one|two|three|four|five|six|seven|eight|nine|\\d)";
    private static final Pattern FIRST_DIGIT_PATTERN = Pattern.compile("^" + DIGIT_PATTERN_STRING + ".*");
    private static final Pattern LAST_DIGIT_PATTERN = Pattern.compile(".*" + DIGIT_PATTERN_STRING + "$");

    @Override
    protected int firstDigit(String line) {
      for (int i = 0; i < line.length(); ++i) {
        var matcher = FIRST_DIGIT_PATTERN.matcher(line.substring(i));
        if (matcher.matches()) {
          return toDigit(matcher.group(1));
        }
      }
      return 0;
    }

    @Override
    protected int lastDigit(String line) {
      for (int i = line.length() - 1; i >= 0; --i) {
        var matcher = LAST_DIGIT_PATTERN.matcher(line.substring(0, i + 1));
        if (matcher.matches()) {
          return toDigit(matcher.group(1));
        }
      }
      return 0;
    }

    private static int toDigit(String digitString) {
      return switch (digitString) {
      case "zero", "0" -> 0;
      case "one", "1" -> 1;
      case "two", "2" -> 2;
      case "three", "3" -> 3;
      case "four", "4" -> 4;
      case "five", "5" -> 5;
      case "six", "6" -> 6;
      case "seven", "7" -> 7;
      case "eight", "8" -> 8;
      case "nine", "9" -> 9;
      default -> throw new IllegalArgumentException();
      };
    }

  }

  abstract static class AoC2023Day1Processor {

    int result(InputStream inputStream) {
      try (var reader = new BufferedReader(new InputStreamReader(inputStream))) {
        int result = 0;
        for (var line = reader.readLine(); line != null; line = reader.readLine()) {
          result += (10 * firstDigit(line) + lastDigit(line));
        }
        return result;
      } catch (IOException e) {
        throw new RuntimeException(e);
      }
    }

    protected abstract int firstDigit(String line);

    protected abstract int lastDigit(String line);

  }

}