private static ulong SellBack(
Dictionary <string, Mapping> elementMapping,
string currentName,
InitializedDictionary <string, ulong> scraps)
{
Mapping current = elementMapping[currentName];
ulong scrapOfElement = scraps[currentName];
ulong cyclesNeeded = scrapOfElement / current.amountProduced;
ulong scrapConsumed = (cyclesNeeded * current.amountProduced);
scraps[currentName] -= scrapConsumed;
if (cyclesNeeded == 0)
{
return(0);
}
ulong maxOres = 0;
foreach (ElementAmount element in current.cost)
{
if (element.name.Equals("ORE"))
{
// Discounts!
return(element.quantity * cyclesNeeded);
}
else
{
scraps[element.name] += (element.quantity * cyclesNeeded);
ulong usingScraps = SellBack(elementMapping, element.name, scraps);
maxOres += usingScraps;
}
}
return(maxOres);
}
private static ulong FindElementCost(
Dictionary <string, Mapping> elementMapping,
string currentName,
ulong amountNeeded,
InitializedDictionary <string, ulong> scraps)
{
Mapping current = elementMapping[currentName];
ulong oreNeeded = 0;
ulong cyclesNeeded = (ulong)Math.Ceiling((float)amountNeeded / (float)current.amountProduced);
// Add leftovers to scraps for future elements
scraps[currentName] += (current.amountProduced * cyclesNeeded) - amountNeeded;
foreach (ElementAmount element in current.cost)
{
if (element.name.Equals("ORE"))
{
// ex. 10 ORE * 3
return(element.quantity * cyclesNeeded);
}
else
{
oreNeeded += FindElementCost(elementMapping, element.name, element.quantity * cyclesNeeded, scraps);
}
}
return(oreNeeded);
}
// sell back scraps to reduce ore costs
// continue attempting to sell until there's no change to balance
private static ulong SellBackAllElements(
Dictionary <string, Mapping> elementMapping,
InitializedDictionary <string, ulong> scraps)
{
bool someChange = true;
ulong oreReceived = 0;
while (someChange)
{
someChange = false;
foreach (var scrap in scraps.Keys.ToList())
{
if (scraps[scrap] > 0)
{
ulong sellback = SellBack(elementMapping, scrap, scraps);
if (sellback > 0)
{
someChange = true;
}
oreReceived += sellback;
}
}
}
return(oreReceived);
}
// Returns a copy of the object
public InitializedDictionary <TKey, TValue> Clone()
{
var clone = new InitializedDictionary <TKey, TValue>();
foreach (TKey key in this.Keys)
{
clone[key] = this._dictionary[key];
}
return(clone);
}
static void Main14(string[] args)
{
string inputProgram = File.ReadAllText(@".\Day14\input.txt");
string[] elementMappingRaw = inputProgram.Trim('\n').Split('\n');
// Build a dictionary of reverse mappings
var elementMapping = new Dictionary <string, Mapping>();
foreach (string rawMapping in elementMappingRaw)
{
string[] mappingSplit = rawMapping.Split(new string[] { " => " }, StringSplitOptions.RemoveEmptyEntries);
var keyElement = new ElementAmount(mappingSplit[1].Trim('\r'));
foreach (string element in mappingSplit[0].Split(new string[] { ", " }, StringSplitOptions.RemoveEmptyEntries))
{
if (!elementMapping.ContainsKey(keyElement.name))
{
elementMapping[keyElement.name] = new Mapping();
elementMapping[keyElement.name].cost = new List <ElementAmount>();
}
elementMapping[keyElement.name].amountProduced = keyElement.quantity;
elementMapping[keyElement.name].cost.Add(new ElementAmount(element));
}
}
ulong totalOre = 1000000000000;
ulong fuelAquired = 0;
var scraps = new InitializedDictionary <string, ulong>();
var scrapsProducedPerCycle = new InitializedDictionary <string, ulong>();
// DFS starting from FUEL
var startingElement = new ElementAmount {
name = "FUEL", quantity = 1
};
ulong oreProducedPerCycleBeforeDiscounts = FindElementCost(elementMapping, startingElement.name, 1, scrapsProducedPerCycle);
ulong oreProducedPerCycle = oreProducedPerCycleBeforeDiscounts;
oreProducedPerCycle -= SellBackAllElements(elementMapping, scrapsProducedPerCycle.Clone());
while (true)
{
// close the gap by running many cycles at once
// this will be a lowerbound
ulong cycles = totalOre / oreProducedPerCycle;
if (cycles == 0)
{
// we don't have enough ore for even one cycle
break;
}
// ore produced
ulong oreProduced = (cycles * oreProducedPerCycleBeforeDiscounts);
// scraps produced
foreach (var scrap in scrapsProducedPerCycle.Keys.ToList())
{
scraps[scrap] += scrapsProducedPerCycle[scrap] * cycles;
}
oreProduced -= SellBackAllElements(elementMapping, scraps);
fuelAquired += cycles;
totalOre -= oreProduced;
}
Console.WriteLine(fuelAquired);
}
