aoc2024/day-07/internal/two/solve.go

package two

import (
	"bytes"
	"fmt"

	log "github.com/sirupsen/logrus"
)

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

	conc := len(equations)
	sumChan := make(chan int)

	for _, equation := range equations {
		go func() {
			var total int
			res, _ := next(equation.target, equation.operands, total, joinOp)
			sumChan <- res
		}()
	}

	var sum int
	for range conc {
		sum += <-sumChan
	}

	return sum, nil
}

func next(target int, operands []int, total int, operator string) (int, bool) {
	if total > target {
		return 0, false
	}

	if len(operands) == 0 {
		if total == target {
			log.Debug(total)
			return total, true
		}
		return 0, false
	}

	switch operator {
	case sumOp:
		total += operands[0]
	case prodOp:
		total *= operands[0]
	case joinOp:
		opStr := fmt.Sprintf("%d%d", total, operands[0])
		total = mustConv(opStr)
	}

	if res, ok := next(target, operands[1:], total, sumOp); ok {
		return res, ok
	}
	if res, ok := next(target, operands[1:], total, prodOp); ok {
		return res, ok
	}
	if res, ok := next(target, operands[1:], total, joinOp); ok {
		return res, ok
	}

	return 0, false
}