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using System;
using System.Collections.Generic;
using System.Linq;
namespace aoc2019
{
internal sealed class Day14 : Day
{
private readonly Dictionary<string, Reaction> reactions;
private Dictionary<string, long> available;
public Day14()
{
reactions = Input
.Select(Reaction.Parse)
.ToDictionary(r => r.product.Name);
}
public override int DayNumber => 14;
private bool Consume(string chem, long quantity)
{
if (quantity <= 0)
throw new ArgumentOutOfRangeException(nameof(quantity));
if (!available.ContainsKey(chem))
available[chem] = 0;
if (available[chem] < quantity && !Produce(chem, quantity - available[chem]))
return false;
available[chem] -= quantity;
return true;
}
private bool Produce(string chem, long quantity)
{
if (chem == "ORE")
return false;
var reaction = reactions[chem];
var reactionCount = (long) Math.Ceiling((double) quantity / reaction.product.Quantity);
foreach (var reactant in reaction.reactants)
if (!Consume(reactant.Name, reactionCount * reactant.Quantity))
return false;
available[chem] = available.GetValueOrDefault(chem) + reactionCount * reaction.product.Quantity;
return true;
}
protected override string Part1()
{
available = new Dictionary<string, long> {{"ORE", long.MaxValue}};
Consume("FUEL", 1);
return $"{long.MaxValue - available["ORE"]}";
}
protected override string Part2()
{
const long capacity = 1_000_000_000_000;
available = new Dictionary<string, long> {{"ORE", capacity}};
Consume("FUEL", 1);
var oreConsumed = capacity - available["ORE"];
while (Produce("FUEL", Math.Max(1, available["ORE"] / oreConsumed)))
{
}
return $"{available["FUEL"] + 1}";
}
private struct Component
{
public string Name { get; set; }
public int Quantity { get; set; }
}
private class Reaction
{
public readonly Component product;
public readonly Component[] reactants;
private Reaction(Component[] reactants, Component product)
{
this.reactants = reactants;
this.product = product;
}
public static Reaction Parse(string s)
{
var ss = s.Split(new[] {", ", " => "}, StringSplitOptions.None);
return new Reaction(
ss.Take(ss.Length - 1).Select(ParseComponent).ToArray(),
ParseComponent(ss[^1])
);
static Component ParseComponent(string s)
{
var spl = s.Split(' ', 2);
return new Component
{
Quantity = int.Parse(spl[0]),
Name = spl[1]
};
}
}
}
}
}
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