Day7.java

package com.sbaars.adventofcode.year19.days;

import com.sbaars.adventofcode.year19.Day2019;
import com.sbaars.adventofcode.year19.intcode.IntcodeComputer;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class Day7 extends Day2019 {
  public Day7() {
    super(7);
  }

  public static void main(String[] args) {
    new Day7().printParts();
  }

  @Override
  public Object part1() {
    var permutations = generatePerm(new ArrayList<>(Arrays.asList(0, 1, 2, 3, 4)));
    List<Long> results = new ArrayList<>();
    for (List<Integer> perm : permutations) {
      long lastVal = 0;
      for (Integer i : perm)
        lastVal = new IntcodeComputer(7, i, lastVal).run();
      results.add(lastVal);

    }
    return results.stream().mapToLong(e -> e).max().getAsLong();
  }

  @Override
  public Object part2() {
    var permutations = generatePerm(new ArrayList<>(Arrays.asList(5, 6, 7, 8, 9)));
    List<Long> results = new ArrayList<>();
    perms:
    for (List<Integer> shuffle : permutations) {
      IntcodeComputer[] computers = new IntcodeComputer[5];
      for (int i = 0; i < computers.length; i++) computers[i] = new IntcodeComputer(7, shuffle.get(i));
      long lastVal = 0;
      while (true) {
        for (IntcodeComputer c : computers) {
          c.addInput(lastVal);
          long thruster = lastVal;
          lastVal = c.run();
          if (lastVal == IntcodeComputer.STOP_CODE) {
            results.add(thruster);
            continue perms;
          }
        }
      }

    }
    return results.stream().mapToLong(e -> e).max().getAsLong();
  }

  public <E> List<List<E>> generatePerm(List<E> original) {
    if (original.isEmpty()) {
      List<List<E>> result = new ArrayList<>();
      result.add(new ArrayList<E>());
      return result;
    }
    E firstElement = original.remove(0);
    List<List<E>> returnValue = new ArrayList<>();
    List<List<E>> permutations = generatePerm(original);
    for (List<E> smallerPermutated : permutations) {
      for (int index = 0; index <= smallerPermutated.size(); index++) {
        List<E> temp = new ArrayList<>(smallerPermutated);
        temp.add(index, firstElement);
        returnValue.add(temp);
      }
    }
    return returnValue;
  }
}