Leaving Code & Coffee

2023/day24/main.go

@@ -14,9 +14,89 @@ func main() {
 }
 
 func part1(inp []string) {
+	//testMin, testMax := float64(7), float64(27) // Test Input
+	testMin, testMax := float64(200000000000000), float64(400000000000000)
+	var all []*hailstone
+	for _, i := range inp {
+		all = append(all, NewHailstone(i))
+	}
+	var count int
+	for i := 0; i < len(all)-1; i++ {
+		for j := i + 1; j < len(all); j++ {
+			x, y := findIntersection(all[i], all[j])
+			if x >= testMin && x <= testMax && y >= testMin && y <= testMax {
+				count++
+			}
+		}
+	}
+
 	fmt.Println("# Part 1")
+	fmt.Println(count)
 }
 
 func part2(inp []string) {
-	fmt.Println("# Part 2")
+	var all []*hailstone
+	for _, i := range inp {
+		all = append(all, NewHailstone(i))
+	}
+	fmt.Println("# Part 2")
+	fmt.Println(findThrow(all))
+}
+
+// https://github.com/rumkugel13/AdventOfCode2023/blob/main/day24.go#L139
+func findThrow(all []*hailstone) int {
+	maybeX, maybeY, maybeZ := []int{}, []int{}, []int{}
+	for i := 0; i < len(all)-1; i++ {
+		for j := i + 1; j < len(all); j++ {
+			a, b := all[i], all[j]
+			if a.DX == b.DX {
+				nextMaybe := findMatchingVelocity(int(b.X-a.X), int(a.DX))
+			}
+		}
+	}
+}
+func findMatchingVelocity(diff, vel int) []int {
+	match := []int{}
+	for v := -1000; v < 1000; v++ {
+		if v != vel && diff%(v-vel) == 0 {
+			match = append(match, v)
+		}
+	}
+	return match
+}
+
+func slope(h *hailstone) float64 {
+	return h.DY / h.DX
+}
+
+func findIntersection(i, j *hailstone) (float64, float64) {
+	if slope(i) == slope(j) {
+		return -1, -1
+	}
+	cx := (j.Y - (j.DY/j.DX)*j.X - (i.Y - (i.DY/i.DX)*i.X)) / (i.DY/i.DX - j.DY/j.DX)
+	perp := !((cx > i.X) == (i.DX > 0) && (cx > j.X) == (j.DX > 0))
+	if perp {
+		return -1, -1
+	}
+
+	y := ((-i.DY/j.DY)*(j.X*j.DY-j.Y*j.DX) + i.X*i.DY - i.Y*i.DX) / ((j.DX * i.DY / j.DY) - i.DX)
+	x := y*j.DX/j.DY + (j.X*j.DY-j.Y*j.DX)/j.DY
+	return x, y
+}
+
+type hailstone struct {
+	X, Y, Z    float64
+	DX, DY, DZ float64
+}
+
+func NewHailstone(inp string) *hailstone {
+	h := hailstone{}
+	fmt.Sscanf(inp, "%f, %f, %f @ %f, %f, %f",
+		&h.X, &h.Y, &h.Z, &h.DX, &h.DY, &h.DZ)
+	return &h
+}
+
+func (h hailstone) String() string {
+	return fmt.Sprintf("%f, %f, %f @ %f, %f, %f",
+		h.X, h.Y, h.Z, h.DX, h.DY, h.DZ)
 }

2023/day24/testinput

@@ -0,0 +1,5 @@
+19, 13, 30 @ -2,  1, -2
+18, 19, 22 @ -1, -1, -2
+20, 25, 34 @ -2, -2, -4
+12, 31, 28 @ -1, -2, -1
+20, 19, 15 @  1, -5, -3