chore: use shoelace and picks theorem
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Go Test / build (pull_request) Successful in 57s
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Go Test / build (pull_request) Successful in 57s
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GPG Key ID:
8B3B0604F164E04F
255
day18/main.go
255
day18/main.go
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@ -3,9 +3,7 @@ package main
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import (
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"bufio"
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_ "embed"
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"encoding/hex"
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"fmt"
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"os"
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"strconv"
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"strings"
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@ -26,8 +24,8 @@ func (r result) String() string { return fmt.Sprintf("%#v", r) }
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func run(scan *bufio.Scanner) (*result, error) {
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var vecs []vec
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var vecs2 []vec
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var vecsPT1 []vector
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var vecsPT2 []vector
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for scan.Scan() {
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text := scan.Text()
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@ -36,199 +34,96 @@ func run(scan *bufio.Scanner) (*result, error) {
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continue
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}
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var s string
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v := vec{}
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s, text, _ = strings.Cut(text, " ")
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v.Direction = direction(s[0])
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s, text, _ = strings.Cut(text, " ")
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v.Steps = aoc.Atoi(s)
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_, text, _ = strings.Cut(text, "#")
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s, _, _ = strings.Cut(text, ")")
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b, _ := hex.DecodeString(s)
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copy(v.Color[:], b)
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vecs = append(vecs, v)
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vecs2 = append(vecs2, fromColor(s))
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v, color := fromLine(text)
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vecsPT1 = append(vecsPT1, v)
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vecsPT2 = append(vecsPT2, fromColor(color))
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}
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return &result{
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valuePT1: findArea(vecs),
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valuePT2: skip("AOC_DAY18P2", func() int { return findArea(vecs2) }),
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valuePT1: findArea(vecsPT1),
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valuePT2: findArea(vecsPT2),
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}, nil
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}
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func findArea(vecs []vec) int {
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var points []point
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var x, y int
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var minX, minY int
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last := direction('S')
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for _, v := range vecs {
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// fmt.Println("pt ", i, v)
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for i := 0; i < v.Steps; i++ {
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switch v.Direction {
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case 'U':
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y++
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case 'D':
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y--
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case 'R':
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x++
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case 'L':
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x--
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}
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// fmt.Println("pt ", i, y, x)
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minX = min(minX, x)
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minY = min(minY, y)
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if len(points) > 0 {
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points[len(points)-1].d = v.Direction
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}
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points = append(points, point{d: v.Direction, w: opposite(v.Direction), x: x, y: y, color: v.Color})
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last = v.Direction
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}
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}
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_ = last
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// points[0].w = last
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points[len(points)-1].d = points[0].w
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adjX := aoc.ABS(min(0, minX))
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adjY := aoc.ABS(min(0, minY))
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fmt.Println("minX", minX, "minY", minY)
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fmt.Println("adjX", adjX, "adjY", adjY)
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trace := make(map[int]map[int]point)
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minX, minY = 0, 0
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maxX, maxY := 0, 0
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for i, p := range points {
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p.x += adjX
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p.y += adjY
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// fmt.Println("raw", i, p.x, p.y, string(p.w), string(p.d))
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maxX = max(maxX, p.x)
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maxY = max(maxY, p.y)
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points[i] = p
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if row, ok := trace[p.y]; true {
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if !ok {
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row = make(map[int]point)
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}
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row[p.x] = p
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trace[p.y] = row
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}
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}
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fmt.Println("maxX", maxX, "maxY", maxY)
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area := 0
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for y := maxY; y >= 0; y-- {
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row, ok := trace[y]
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if !ok {
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continue
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}
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var last direction
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p := row[0]
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last = p.d
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inLoop := false
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for x := 0; x <= maxX; x++ {
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if p, ok := row[x]; ok {
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// fmt.Println("vec", string(p.w), string(p.d))
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switch string([]rune{rune(p.w), rune(p.d)}) {
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case "LD", "DL", "UD", "DU", "RD", "UU", "DR":
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inLoop = !inLoop
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}
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if last != p.d {
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last = p.d
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}
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// fmt.Print(string(p.w)+string(p.d))
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// On loop
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area++
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continue // 203338
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}
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last = direction('0')
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if inLoop {
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area++
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// fmt.Print("XX")
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// } else {
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// fmt.Print("..")
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}
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}
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// fmt.Println("")
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fmt.Println(y, area)
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}
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return area
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type vector struct {
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offset point
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scale int
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}
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type direction rune
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type point [2]int
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const (
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U direction = 'U'
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D direction = 'D'
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L direction = 'L'
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R direction = 'R'
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)
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func (p point) add(a point) point {
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return point{p[0] + a[0], p[1] + a[1]}
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}
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func (p point) scale(m int) point {
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return point{p[0] * m, p[1] * m}
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}
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func opposite(d direction) direction {
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switch d {
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case U:
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return D
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case D:
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return U
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case L:
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return R
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case R:
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return L
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// numPoints the number of the points inside an outline plus the number of points in the outline
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func numPoints(outline []point, borderLength int) int {
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// shoelace - find the float area in a shape
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sum := 0
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for _, p := range pairwise(outline) {
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row1, col1 := p[0][0], p[0][1]
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row2, col2 := p[1][0], p[1][1]
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sum += row1*col2 - row2*col1
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}
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return '0'
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area := sum / 2
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// pick's theorem - find the number of points in a shape given its area
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return (aoc.ABS(area) - borderLength/2 + 1) + borderLength
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}
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type vec struct {
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Direction direction
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Steps int
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Color [3]byte
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}
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type point struct {
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w direction
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d direction
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x, y int
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color [3]byte
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}
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func fromColor(c string) vec {
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steps, _ := strconv.ParseInt(c[:5], 16, 64)
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d := '_'
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switch c[5] {
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case '0':
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d = 'R'
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case '1':
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d = 'D'
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case '2':
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d = 'L'
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case '3':
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d = 'U'
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func pairwise[T any](arr []T) [][2]T {
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var pairs [][2]T
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for i := range arr[:len(arr)-1] {
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pairs = append(pairs, [2]T{arr[i], arr[i+1]})
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}
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return pairs
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}
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return vec{
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Direction: direction(d),
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Steps: int(steps),
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var OFFSET = map[string]point{
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"R": {0, 1},
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"D": {1, 0},
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"L": {0, -1},
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"U": {-1, 0},
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}
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var OFFSET_INDEXES = maps.Values(OFFSET)
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func fromLine(text string) (vector, string) {
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v := vector{}
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s, text, _ := strings.Cut(text, " ")
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v.offset = OFFSET[s]
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s, text, _ = strings.Cut(text, " ")
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v.scale = aoc.Atoi(s)
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_, text, _ = strings.Cut(text, "(#")
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s, _, _ = strings.Cut(text, ")")
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return v, s
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}
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func fromColor(c string) vector {
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scale, _ := strconv.ParseInt(c[:5], 16, 64)
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offset := OFFSET_INDEXES[c[5]-'0']
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return vector{
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offset: offset,
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scale: int(scale),
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}
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}
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func skip[T any](env string, fn func() T) T {
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var zero T
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if e, err := strconv.ParseBool(os.Getenv(env)); err == nil && e {
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return zero
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func findArea(vecs []vector) int {
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shoelace := []point{{0,0}}
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borderLength := 0
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for _, vec := range vecs {
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scaled_offset := vec.offset.scale(vec.scale)
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shoelace = append(shoelace, shoelace[len(shoelace)-1].add(scaled_offset))
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borderLength += vec.scale
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}
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return fn()
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return numPoints(shoelace, borderLength)
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}
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@ -3,7 +3,6 @@ package main
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import (
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"bufio"
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"bytes"
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"os"
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"testing"
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_ "embed"
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@ -33,13 +32,11 @@ func TestSolution(t *testing.T) {
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is := is.New(t)
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scan := bufio.NewScanner(bytes.NewReader(input))
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os.Setenv("AOC_DAY18P2", "1")
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result, err := run(scan)
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is.NoErr(err)
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t.Log(result)
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is.True(result.valuePT1 < 68834) // first attempt too high.
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is.Equal(result.valuePT1, 46334)
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is.Equal(result.valuePT2, 0)
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is.Equal(result.valuePT2, 102000662718092)
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}
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