Day4.java

package com.sbaars.adventofcode.year19.days;

import com.sbaars.adventofcode.year19.Day2019;

import java.util.stream.IntStream;

public class Day4 extends Day2019 {
  public Day4() {
    super(4);
  }

  public static void main(String[] args) {
    new Day4().printParts();
  }

  @Override
  public Object part1() {
    return checkPasswords(false);
  }

  @Override
  public Object part2() {
    return checkPasswords(true);
  }

  public long meetsCriteria(int lowerBound, int higherBound, boolean checkGroup) {
    return IntStream.range(lowerBound, higherBound + 1).filter(e -> meetsCriteria(e, checkGroup)).count();
  }

  public boolean meetsCriteria(int input, boolean checkGroup) {
    int lastSeen = 10, current, adjacentTheSame = -2, skip = 10;

    for (int i = 0; input > 0; i++) {
      current = input % 10;
      if (skip != current && current == lastSeen) {
        if (checkGroup && adjacentTheSame + 1 == i) {
          adjacentTheSame = -2;
          skip = current;
        } else if (adjacentTheSame == -2) {
          adjacentTheSame = i;
        }
      }
      if (lastSeen < current)
        return false;
      lastSeen = current;
      input /= 10;
    }

    return adjacentTheSame != -2;
  }

  private int checkPasswords(boolean checkGroup) {
    return Math.toIntExact(meetsCriteria(372037, 905157, checkGroup));
  }

}