aoc2024/day-11/internal/one/solve.go

package one

import (
	"bytes"

	log "github.com/sirupsen/logrus"

	"github.com/onyx-and-iris/aoc2024/day-11/internal/queue"
)

const blinks = 25
const magic = 2024

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

	old := queue.New[int]()
	for _, n := range numbers {
		old.Enqueue(n)
	}
	log.Debug(old)

	for range blinks {
		next := queue.New[int]()
		for !old.IsEmpty() {
			n := old.Dequeue()
			left, right, ok := applyRules(n)
			if ok {
				next.Enqueue(left)
			}
			next.Enqueue(right)
		}

		old = next
		log.Debug(old)
	}

	return old.Len(), nil
}

func applyRules(num int) (int, int, bool) {
	switch num := num; {
	case num == 0:
		return 0, 1, false
	case lenItoa(num)%2 == 0:
		left, right := splitNumber(num)
		return left, right, true
	default:
		return 0, num * magic, false
	}
}