Day14.java

package com.sbaars.adventofcode.year19.days;

import com.sbaars.adventofcode.common.HasRecursion;
import com.sbaars.adventofcode.common.map.LongCountMap;
import com.sbaars.adventofcode.year19.Day2019;

import java.util.Arrays;

public class Day14 extends Day2019 implements HasRecursion {

  private final Trade[] trades;

  public Day14() {
    super(14);
    this.trades = dayStream().map(Trade::new).toArray(Trade[]::new);
  }

  public static void main(String[] args) {
    new Day14().printParts();
  }

  @Override
  public Object part1() {
    return findCost(new Item(1, "FUEL"), new LongCountMap<>());
  }

  private Trade getTrade(String key) {
    return Arrays.stream(trades).filter(e -> e.output.item.equals(key)).findAny().get();
  }

  private long findCost(Item buyingItem, LongCountMap<String> leftOver) {
    if (buyingItem.item.equals("ORE"))
      return buyingItem.amount;
    else if (buyingItem.amount <= leftOver.get(buyingItem.item)) {
      leftOver.increment(buyingItem.item, -buyingItem.amount);
      return 0;
    }
    buyingItem.amount -= leftOver.get(buyingItem.item);
    leftOver.put(buyingItem.item, 0L);

    return performTrade(buyingItem, leftOver);
  }

  private long performTrade(Item buyingItem, LongCountMap<String> leftOver) {
    Trade fuelTrade = getTrade(buyingItem.item);
    long timesApplied = (long) Math.ceil((double) buyingItem.amount / (double) fuelTrade.output.amount);
    long totalCost = 0;
    for (Item cost : fuelTrade.input)
      totalCost += findCost(new Item(cost.amount * timesApplied, cost.item), leftOver);
    leftOver.increment(buyingItem.item, fuelTrade.output.amount * timesApplied - buyingItem.amount);
    return totalCost;
  }

  @Override
  public Object part2() {
    long oreLeft = 1000000000000L;
    long fuel = 1;
    while (true) {
      long cost = findCost(new Item(fuel + 1, "FUEL"), new LongCountMap<>());
      if (cost > oreLeft) {
        return fuel;
      } else {
        fuel = Math.max(fuel + 1, (fuel + 1) * oreLeft / cost);
      }
    }
  }

  class Trade {
    private final Item[] input;
    private final Item output;

    public Trade(String trade) {
      String[] inputOutput = trade.split(" => ");
      input = Arrays.stream(inputOutput[0].split(", ")).map(Item::new).toArray(Item[]::new);
      output = new Item(inputOutput[1]);
    }
  }

  class Item {
    private final String item;
    private long amount;

    public Item(String item) {
      String[] i = item.split(" ");
      amount = Integer.parseInt(i[0]);
      this.item = i[1];
    }

    public Item(long i, String string) {
      amount = i;
      item = string;
    }
  }
}