aoc2024/day-22/internal/two/solve.go

package two

import (
	"bytes"
	"math"

	"github.com/onyx-and-iris/aoc2024/day-22/internal/randomiser"
)

const numIterations = 2000

func Solve(buf []byte) (int, error) {
	r := bytes.NewReader(buf)
	secrets, err := parseLines(r)
	if err != nil {
		return 0, err
	}

	conc := len(secrets)
	done := make(chan bool)

	cache := newSequenceCache()
	for _, secret := range secrets {
		go func() {
			seen := make(map[sequence]struct{})
			sequence := sequence{math.MaxInt, math.MaxInt, math.MaxInt, math.MaxInt}

			randomiser := randomiser.New(secret)
			for range numIterations {
				prev := lastDigit(randomiser.Secret())
				randomiser.Randomise()

				sequence.shift(prev - lastDigit(randomiser.Secret()))

				_, ok := seen[sequence]
				if !ok {
					seen[sequence] = struct{}{}
					cache.upsert(sequence, lastDigit(randomiser.Secret()))
				}
			}
			done <- true
		}()
	}

	for range conc {
		<-done
	}

	max := 0
	for _, sum := range cache.data {
		if sum > max {
			max = sum
		}
	}
	return max, nil
}