part2.go

func runPart() error {
	start := time.Now()
	filename := "day6//input.txt"
	races, err := loadRace(filename)
	if err != nil {
		return err
	}
	waysComb := int64(1)
	for _, race := range races {
		waysComb *= calculus(race)
	}
	fmt.Printf("\nwaysComb %d", waysComb)
	fmt.Printf("\nexecution time: %s", time.Since(start).String())
	return nil
}

func calculus(race *Race) int64 {
	// x*2 - race.Duration * x + race.RecordDistance
	D := race.Duration*race.Duration - 4*race.RecordDistance
	DSQRT := math.Sqrt(float64(D))
	answer1 := int64((float64(race.Duration) + DSQRT) / 2)
	fmt.Printf("\n answer1: %d", int(answer1))
	answer2 := int64((float64(race.Duration) - DSQRT) / 2)
	fmt.Printf("\n answer2: %d", int(answer2))
	return max(answer2, answer1) - min(answer2, answer1)
}