Day12.java

package com.sbaars.adventofcode.year19.days;

import com.sbaars.adventofcode.year19.Day2019;
import static com.sbaars.adventofcode.util.AoCUtils.gcd;
import java.util.Arrays;
import java.util.Collections;
import java.util.HashSet;

public class Day12 extends Day2019 {
  int[][] moons = {{-5, 6, -11}, {-8, -4, -2}, {1, 16, 4}, {11, 11, -4}};
  int[][] velocity = {{0, 0, 0}, {0, 0, 0}, {0, 0, 0}, {0, 0, 0}};

  public Day12() {
    super(12);
  }

  public static void main(String[] args) {
    new Day12().printParts();
  }

  public static long lcm(long a, long b) {
    return a * (b / gcd(a, b));
  }

  public static long lcm(long[] input) {
    long result = input[0];
    for (int i = 1; i < input.length; i++) result = lcm(result, input[i]);
    return result;
  }

  @Override
  public Object part1() {
    for (int n = 0; n < 1000; n++) {
      determineVelocity();
      moveMoonsUsingVelocity();
    }
    int[] res = new int[moons.length];
    for (int i = 0; i < res.length; i++) {
      res[i] = Arrays.stream(moons[i]).map(Math::abs).sum() * Arrays.stream(velocity[i]).map(Math::abs).sum();
    }
    return Arrays.stream(res).sum();
  }

  @Override
  public Object part2() {
    var sets = Collections.nCopies(moons[0].length, new HashSet<>());
    long[] res = new long[sets.size()];
    for (long n = 0; true; n++) {
      determineVelocity();
      moveMoonsUsingVelocity();

      for (int i = 0; i < sets.size(); i++) {
        if (res[i] == 0 && !sets.get(i).add(Arrays.asList(moons[0][i], moons[1][i], moons[2][i], moons[3][i], velocity[0][i], velocity[1][i], velocity[2][i], velocity[3][i]))) {
          res[i] = n;
          if (Arrays.stream(res).noneMatch(x -> x == 0)) {
            return lcm(res);
          }
        }
      }
    }
  }

  private void moveMoonsUsingVelocity() {
    for (int i = 0; i < moons.length; i++) {
      for (int j = 0; j < moons[0].length; j++) {
        moons[i][j] += velocity[i][j];
      }
    }
  }

  private void determineVelocity() {
    for (int i = 0; i < moons.length; i++) {
      for (int j = i + 1; j < moons.length; j++) {
        for (int dim = 0; dim < moons[0].length; dim++) {
          int moon1 = moons[i][dim], moon2 = moons[j][dim];
          if (moon1 < moon2) {
            velocity[i][dim]++;
            velocity[j][dim]--;
          } else if (moon1 > moon2) {
            velocity[i][dim]--;
            velocity[j][dim]++;
          }
        }
      }
    }
  }

  short[][] copy(short[][] arr) {
    short[][] myInt = new short[arr.length][];
    for (int i = 0; i < arr.length; i++)
      myInt[i] = arr[i].clone();
    return myInt;
  }
}