public override (string message, object answer) SolvePart2()
{
const long DeckSize = 119_315_717_514_047;
const long Iterations = 101_741_582_076_661;
DeckData passData = new DeckData(DeckSize);
// Determine the result of a single shuffle pass on the deck state
foreach (Technique technique in _techniques)
{
technique.Apply(passData);
}
// Calculate the result of applying the shuffle many times
DeckData finalData = new DeckData(DeckSize);
finalData.increment = MathUtil.ModPower(passData.increment, Iterations, DeckSize);
finalData.offset = (passData.offset * (1 - finalData.increment) *
MathUtil.ModPower(1 - passData.increment, DeckSize - 2, DeckSize)) % DeckSize;
BigInteger card = (finalData.offset + (finalData.increment * 2020)) % DeckSize;
return($"Card 2020 after {Iterations} shuffles:", card);
}
public abstract void Apply(DeckData deck);
public override void Apply(DeckData deck)
{
deck.increment *= -1;
deck.offset += deck.increment;
}
