day24, example

day24/lines.go

@@ -0,0 +1,147 @@
+package day24
+
+import (
+	"log"
+	"os"
+	"strconv"
+	"strings"
+)
+
+const (
+	CoordMin int = 7
+	CoordMax int = 27
+)
+
+type Point struct {
+	x, y, Z int
+}
+
+type HailParam struct {
+	p0, p1 Point
+	Dx, Dy, Dz int
+	line string
+}
+func (h HailParam)String() string {
+	return "(" + h.line + ")"
+}
+
+func CheckPairwiseIntersections(hails []HailParam) (totalIntersections int) {
+	for i, hail := range hails {
+		for j := i+1; j < len(hails); j++ {
+			otherHail := hails[j]
+			intersect := CheckTaskIntersection(hail, otherHail)
+			if intersect {
+				totalIntersections += 1
+			}
+		}
+	}
+	return
+}
+
+func CheckTaskIntersection(h1, h2 HailParam) (doIntersect bool) {
+	log.Printf("intersecting %+v and %+v\n", h1, h2)
+	x, y, intersectAtAll := IntersectByTwoPoints(h1, h2)
+	if !intersectAtAll {
+		log.Printf("no intersection at all\n")
+		return false
+	}
+	if x < float64(CoordMin) || x > float64(CoordMax) ||
+		y < float64(CoordMin) || y > float64(CoordMax) {
+		log.Printf("intersect at %f %f but outside of area\n", x, y)
+		return false // outside of area
+	}
+	isH1Future := h1.FloatPointInFuture(x,y)
+	isH2Future := h2.FloatPointInFuture(x,y)
+
+	if !isH1Future {
+		log.Printf("in the past for h1\n")
+	}
+	if !isH2Future {
+		log.Printf("in the past for h2\n")
+	}
+
+	if !isH1Future || !isH2Future {
+		return false
+	}
+
+	log.Println("intersect inside of the area")
+	return true
+}
+
+// in 2d only
+func IntersectByTwoPoints(h1, h2 HailParam) (intersectionX, intersectoinY float64, isIntersecting bool) {
+	p1 := h1.p0
+	p2 := h1.p1
+	p3 := h2.p0
+	p4 := h2.p1
+
+	denominator := (p1.x - p2.x)*(p3.y - p4.y) - (p1.y - p2.y)*(p3.x - p4.x)
+	if denominator == 0 {
+		return 0, 0, false
+	}
+
+	divisibleX := (p1.x * p2.y - p1.y * p2.x)*(p3.x - p4.x) - (p1.x - p2.x)*(p3.x * p4.y - p3.y * p4.x)
+	divisibleY := (p1.x * p2.y - p1.y * p2.x)*(p3.y - p4.y) - (p1.y - p2.y)*(p3.x * p4.y - p3.y * p4.x)
+
+	x := float64(divisibleX) / float64(denominator)
+	y := float64(divisibleY) / float64(denominator)
+
+	return x, y, true
+}
+
+func (h HailParam)PointInFuture(p Point) bool {
+	xPositiveSteps := (p.x - h.p0.x) * h.Dx >= 0
+	yPositiveSteps := (p.y - h.p0.y) * h.Dy >= 0
+	zPositiveSteps := (p.Z - h.p0.Z) * h.Dz >= 0
+	return xPositiveSteps && yPositiveSteps && zPositiveSteps
+}
+func (h HailParam)FloatPointInFuture(x, y float64) bool {
+	xPositiveSteps := (x - float64(h.p0.x)) * float64(h.Dx) >= 0
+	yPositiveSteps := (y - float64(h.p0.y)) * float64(h.Dy) >= 0
+	return xPositiveSteps && yPositiveSteps
+}
+
+// 19, 13, 30 @ -2,  1, -2
+func ReadHailLine(line string) (h HailParam) {
+	h.line = line
+	line = strings.ReplaceAll(line, "@", "")
+	line = strings.ReplaceAll(line, ",", "")
+	fields := strings.Fields(line)
+
+	h.p0.x = AtoIOrPanic(fields[0])
+	h.p0.y = AtoIOrPanic(fields[1])
+	h.p0.Z = AtoIOrPanic(fields[2])
+	h.Dx = AtoIOrPanic(fields[3])
+	h.Dy = AtoIOrPanic(fields[4])
+	h.Dz = AtoIOrPanic(fields[5])
+
+	h.p1.x = h.p0.x + h.Dx
+	h.p1.y = h.p0.y + h.Dy
+	h.p1.Z = h.p0.Z + h.Dz
+
+	return
+}
+
+func ReadHailFile(filename string) []HailParam {
+	bytes, err := os.ReadFile(filename)
+	if err != nil {
+		panic(err)
+	}
+	text := strings.TrimSpace(string(bytes))
+	lines := strings.Split(text, "\n")
+	result := make([]HailParam, len(lines))
+
+	for i, line := range lines {
+		result[i] = ReadHailLine(line)
+	}
+
+	return result
+}
+
+func AtoIOrPanic(str string) (num int) {
+	num, err := strconv.Atoi(str)
+	if err != nil {
+		panic(err)
+	}
+	return
+}