feat: progress

pkg/car_fleet/main.go

@@ -0,0 +1,85 @@
+package car_fleet
+
+import (
+	"fmt"
+	"math"
+	"slices"
+)
+
+type Car struct {
+	position int
+	speed    int
+}
+
+func (c Car) CollidesInto(o Car) float64 {
+	if c.speed == o.speed {
+		return math.Inf(1)
+	}
+	return float64(c.position-o.position) / float64(o.speed-c.speed)
+}
+
+func (c Car) At(time int) int {
+	return c.position + c.speed*time
+}
+
+type CarSpace struct {
+	car  Car
+	from float64
+	to   float64
+}
+
+func (s CarSpace) Contains(point float64) bool {
+	return point >= float64(s.from) && point <= float64(s.to)
+}
+
+func sortByInversePosition(a Car, b Car) int {
+	return b.position - a.position
+}
+
+func CarFleet(target int, position []int, speed []int) int {
+	cars := []Car{}
+	ends := map[int]bool{}
+
+	for i := range position {
+		cars = append(cars, Car{
+			position: position[i],
+			speed:    speed[i],
+		})
+	}
+
+	slices.SortFunc(cars, sortByInversePosition)
+	stack := []CarSpace{}
+
+	for _, car := range cars {
+		for {
+			fmt.Println(car, stack)
+			if len(stack) == 0 {
+				stack = append(stack, CarSpace{
+					car:  car,
+					from: 0,
+					to:   float64(target),
+				})
+				break
+			}
+
+			top := stack[len(stack)-1]
+			time := car.CollidesInto(top.car)
+			if top.Contains(time) {
+				stack[len(stack)-1].from = time
+				stack = append(stack, CarSpace{
+					car:  car,
+					from: 0,
+					to:   time,
+				})
+				break
+			}
+
+			stack = stack[:len(stack)-1]
+		}
+
+		ending_at := stack[0].car.At(target)
+		ends[ending_at] = true
+	}
+
+	return len(ends)
+}

pkg/car_fleet/main_test.go

@@ -0,0 +1,44 @@
+package car_fleet_test
+
+import (
+	"testing"
+
+	"git.maximhutz.com/practice/pkg/car_fleet"
+	"github.com/stretchr/testify/assert"
+)
+
+func Test1(t *testing.T) {
+	target := 12
+	position := []int{10, 8, 0, 5, 3}
+	speed := []int{2, 4, 1, 1, 3}
+	output := 3
+
+	assert.Equal(t, output, car_fleet.CarFleet(target, position, speed))
+}
+
+func Test2(t *testing.T) {
+	target := 10
+	position := []int{3}
+	speed := []int{3}
+	output := 1
+
+	assert.Equal(t, output, car_fleet.CarFleet(target, position, speed))
+}
+
+func Test3(t *testing.T) {
+	target := 100
+	position := []int{0, 2, 4}
+	speed := []int{4, 2, 1}
+	output := 1
+
+	assert.Equal(t, output, car_fleet.CarFleet(target, position, speed))
+}
+
+func Test4(t *testing.T) {
+	target := 10
+	position := []int{6, 8}
+	speed := []int{3, 2}
+	output := 2
+
+	assert.Equal(t, output, car_fleet.CarFleet(target, position, speed))
+}