package day6

import (
	"math"
	"strings"

	"gitea.paas.celticinfo.fr/oabrivard/aoc2023/utils"
)

func RaceWinsCount(lines []string) int64 {
	result := int64(1)
	times := utils.ParseInt64Array(strings.TrimPrefix(lines[0], "Time: "), " ")
	dists := utils.ParseInt64Array(strings.TrimPrefix(lines[1], "Distance: "), " ")

	for i, t := range times {
		d := dists[i]

		// Solve -x^2 + tx - d > 0

		// delta = b^2 - 4ac
		delta := utils.Int64Pow(t, 2) - 4*d

		// x1 = (-t + sqrt(delta)) / -2
		// x2 = (-t - sqrt(delta)) / -2
		x1 := (-float64(t) + math.Sqrt(float64(delta))) / -2.0
		x2 := (-float64(t) - math.Sqrt(float64(delta))) / -2.0
		x1_int := math.Ceil(x1)
		x2_int := math.Floor(x2)
		if x1_int == x1 {
			x1_int++
		}
		if x2_int == x2 {
			x2_int--
		}
		count := int64(x2_int) - int64(x1_int) + 1
		result *= count
	}

	return result
}