Completed both parts of Day 6 puzzle

day6/day6.go

@@ -0,0 +1,40 @@
+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
+}

day6/day6_test.go

@@ -0,0 +1,56 @@
+package day6
+
+import (
+	"testing"
+)
+
+func TestRaceWinsCount(t *testing.T) {
+	lines := []string{
+		"Time:      7  15   30",
+		"Distance:  9  40  200",
+	}
+
+	result := RaceWinsCount(lines)
+
+	if result != 288 {
+		t.Fatalf("expected 288, got %v", result)
+	}
+}
+
+func TestRaceWinsCountWithInput(t *testing.T) {
+	lines := []string{
+		"Time:        54     81     70     88",
+		"Distance:   446   1292   1035   1007",
+	}
+	result := RaceWinsCount(lines)
+
+	if result != 2065338 {
+		t.Fatalf("expected 2065338, got %v", result)
+	}
+}
+
+func TestRaceWinsCount2(t *testing.T) {
+	lines := []string{
+		"Time:      71530",
+		"Distance:  940200",
+	}
+
+	result := RaceWinsCount(lines)
+
+	if result != 71503 {
+		t.Fatalf("expected 71503, got %v", result)
+	}
+}
+
+func TestRaceWinsCountWithInput2(t *testing.T) {
+	lines := []string{
+		"Time:      54817088",
+		"Distance:  446129210351007",
+	}
+
+	result := RaceWinsCount(lines)
+
+	if result != 34934171 {
+		t.Fatalf("expected 34934171, got %v", result)
+	}
+}

utils/utils.go

@@ -73,3 +73,13 @@ func IntPow(x int, y int) int {
 
 	return result
 }
+
+func Int64Pow(x int64, y int64) int64 {
+	result := int64(1)
+
+	for i := int64(0); i < y; i++ {
+		result *= x
+	}
+
+	return result
+}