question 6

go/go.mod

@@ -0,0 +1,3 @@
+module advent-of-code-2024
+
+go 1.23

go/go.work

@@ -0,0 +1,3 @@
+go 1.23
+
+use .

go/question6/input.go

@@ -0,0 +1,3 @@
+package main
+
+const realInput = "...#........................................#........#.................#............#.#.......................#...............#..#\n...#........#.....#..................................................................................#......#..#..................\n.................#.......................#.#........#......#...........................................#...#..........#...........\n..................#..................#...#.....................................#........#.........................................\n...#.....#.......#..............#.#....##.............#....##......................................#...................#..........\n...#..........................................................................................................................#...\n..#..#.............#.....#...............#.......#..............................................#....#............................\n......................#..#...............#...................#....#..........................#...#............#...#....##.........\n..#.#.........#................#............#............#.#.......#................#....#..#.....................................\n.......................................................................#.....................................#...........#........\n...........#.....................................................................#.................................#......#.......\n...#.........#....................................................#..............#.............#..........#.......................\n.................................................................................................#................................\n..................................#.#.#...#.......#.............#.......................#..#.......................#.#............\n.......................#.........................................#..........#...#.....#....................................#......\n.......#.......#.#...........#......................#.....#..#...#.#...............#.............................#...#............\n............##...#......#.........#......#............................................................#.........#..............#..\n..#........................................#........##..#...............................................................#.........\n...........#..............##................................................................................#.....................\n..#................................................................................#..............#...............................\n...................................##..............#..........................#.......#..#...............#........#...............\n....#............#.........................#................................................................#........#............\n............#.....................................................................#.............................................#.\n............#..........#.......#...........#.#......#..............#.........#.......................................#......#.....\n..#...............................................#..................................#.............................#.............#\n.........................................................................#........#................#......#.......#....#........#.\n.......................................................................#.....##.................................................#.\n..............#.............#...........................#...#..#....................................................#.............\n.......#..........................#.......................###..................................#.....................#..#.........\n................#.................#.............#......................................................................#........#.\n.#.....#................#......................................................................#................#.................\n................................#........................#........#..#........................#...................................\n..............................................................................................#.....................#.........#...\n..................#.................#.........................#.....#................#............................................\n......#...................#...#...................#..................#...........................#......###...................#...\n.............................##.....#..............#..............................................................#....#..........\n......#..................#....................................................###....................#..............#.............\n............#...#..................#........#.............#..............................#......Line truncated

go/question6/main.go

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+package main
+
+import (
+	"fmt"
+	"strings"
+)
+
+const mockInput = "....#.....\n.........#\n..........\n..#.......\n.......#..\n..........\n.#..^.....\n........#.\n#.........\n......#..."
+
+type Direction uint8
+
+const (
+	UP Direction = iota
+	RIGHT
+	DOWN
+	LEFT
+)
+
+func (d Direction) Next() Direction {
+	return (d + 1) % 4
+}
+
+func (d Direction) NextPoint(p *Point) *Point {
+	if d == UP {
+		return &Point{p.x, p.y - 1}
+	}
+	if d == DOWN {
+		return &Point{p.x, p.y + 1}
+	}
+	if d == LEFT {
+		return &Point{p.x - 1, p.y}
+	}
+	return &Point{p.x + 1, p.y}
+}
+
+type Point struct {
+	x, y int
+}
+
+func (p *Point) String() string {
+	return fmt.Sprintf("(%d, %d)", p.x, p.y)
+}
+
+type Map struct {
+	data   []rune
+	width  int
+	height int
+}
+
+func (m *Map) isInbound(point *Point) bool {
+	return point.x >= 0 && point.x < m.width && point.y >= 0 && point.y < m.width
+}
+
+func (m *Map) Get(point *Point) (rune, bool) {
+	if !m.isInbound(point) {
+		return 0, false
+	}
+	idx := point.x + m.width*point.y
+	return m.data[idx], true
+}
+
+func (m *Map) Set(point *Point, r rune) {
+	idx := point.x + m.width*point.y
+	m.data[idx] = r
+}
+
+type Guard struct {
+	position  *Point
+	direction Direction
+}
+
+func (g *Guard) String() string {
+	return fmt.Sprintf("%s[%d]", g.position, g.direction)
+}
+
+func FindGuard(input string) *Guard {
+	m := NewMap(input)
+	input = strings.ReplaceAll(input, "\n", "")
+	rawIndex := strings.Index(input, "^")
+
+	x := rawIndex % m.width
+	y := rawIndex / m.width
+	return &Guard{&Point{x, y}, UP}
+}
+
+func NewMap(input string) *Map {
+	if !strings.HasSuffix(input, "\n") {
+		input += "\n"
+	}
+	input = strings.ReplaceAll(input, "^", ".")
+	width := strings.Index(input, "\n")
+	height := strings.Count(input, "\n")
+	data := []rune(strings.ReplaceAll(input, "\n", ""))
+	return &Map{data, width, height}
+}
+
+func isWall(v rune) bool {
+	return v == '#'
+}
+
+func nextGuard(m *Map, guard *Guard) (*Guard, bool) {
+	nextPosition := guard.direction.NextPoint(guard.position)
+	if v, ok := m.Get(nextPosition); !ok {
+		return nil, false
+	} else if isWall(v) {
+		return &Guard{guard.position, guard.direction.Next()}, true
+	} else {
+		return &Guard{nextPosition, guard.direction}, true
+	}
+}
+
+func WalkGuard(m *Map, guard *Guard) chan *Guard {
+	out := make(chan *Guard)
+	go func() {
+		for guard, ok := guard, true; ok; guard, ok = nextGuard(m, guard) {
+			out <- guard
+		}
+		close(out)
+	}()
+	return out
+}
+
+func UniquePoints(guards chan *Guard) chan *Guard {
+	out := make(chan *Guard)
+	m := make(map[int]map[int]bool)
+
+	go func() {
+		for guard := range guards {
+			p := guard.position
+			if v, ok := m[p.x]; ok {
+				if _, ok2 := v[p.y]; ok2 {
+					continue
+				} else {
+					m[p.x][p.y] = true
+				}
+			} else {
+				m[p.x] = make(map[int]bool)
+				m[p.x][p.y] = true
+			}
+			out <- guard
+		}
+		close(out)
+	}()
+	return out
+}
+
+func Question6A(input string) int {
+	m := NewMap(input)
+	guard := FindGuard(input)
+	i := 0
+	for _ = range UniquePoints(WalkGuard(m, guard)) {
+		i += 1
+	}
+	return i
+}
+
+func checkIfGuardMakesALoop(m *Map, guard *Guard) <-chan bool {
+	out := make(chan bool)
+	go func() {
+		out <- isGuardMakingALoop(m, guard)
+		close(out)
+	}()
+	return out
+
+}
+
+func Question6B(input string) int {
+	m := NewMap(input)
+	guard := FindGuard(input)
+	chans := make([]<-chan bool, 0)
+	possibleWallPositions := Rest(GetPoints(UniquePoints(WalkGuard(m, guard))))
+	for point := range possibleWallPositions {
+		newMap := placeBlock(m, point)
+		chans = append(chans, checkIfGuardMakesALoop(newMap, guard))
+	}
+
+	sum := 0
+	for _, f := range chans {
+		if <-f {
+			sum++
+		}
+	}
+	return sum
+}
+
+func isGuardMakingALoop(m *Map, guard *Guard) bool {
+	visited := make(map[int]map[int]map[Direction]bool)
+	for guard := range WalkGuard(m, guard) {
+		if _, ok := visited[guard.position.x]; ok {
+			if _, ok2 := visited[guard.position.x][guard.position.y]; ok2 {
+				if _, ok3 := visited[guard.position.x][guard.position.y][guard.direction]; ok3 {
+					return true
+				} else {
+					visited[guard.position.x][guard.position.y][guard.direction] = true
+				}
+			} else {
+				visited[guard.position.x][guard.position.y] = make(map[Direction]bool)
+				visited[guard.position.x][guard.position.y][guard.direction] = true
+			}
+		} else {
+			visited[guard.position.x] = make(map[int]map[Direction]bool)
+			visited[guard.position.x][guard.position.y] = make(map[Direction]bool)
+			visited[guard.position.x][guard.position.y][guard.direction] = true
+		}
+	}
+	return false
+}
+
+func placeBlock(m *Map, point *Point) *Map {
+	data := make([]rune, len(m.data))
+	copy(data, m.data)
+	ret := &Map{data, m.width, m.height}
+	ret.Set(point, rune('#'))
+	return ret
+}
+
+func Rest(points <-chan *Point) <-chan *Point {
+	out := make(chan *Point)
+	go func() {
+		first := true
+		for p := range points {
+			if first {
+				first = false
+				continue
+			}
+			out <- p
+		}
+		close(out)
+	}()
+	return out
+
+}
+
+func GetPoints(guards <-chan *Guard) <-chan *Point {
+	out := make(chan *Point)
+	go func() {
+		for guard := range guards {
+			out <- guard.position
+		}
+		close(out)
+	}()
+	return out
+
+}
+
+func main() {
+	//answer6A := Question6A(realInput)
+	//fmt.Printf("The answer to question 6A is %d\n", answer6A)
+
+	answer6B := Question6B(realInput)
+	fmt.Printf("The answer to question 6A is %d\n", answer6B)
+}