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| 1 | +// [Day 10: Hoof It](https://adventofcode.com/2024/day/10) |
| 2 | + |
| 3 | +package main |
| 4 | + |
| 5 | +import ( |
| 6 | + "container/list" |
| 7 | + "fmt" |
| 8 | + "log" |
| 9 | + "os" |
| 10 | + "strings" |
| 11 | + "time" |
| 12 | +) |
| 13 | + |
| 14 | +const ( |
| 15 | + bottom = byte('0') |
| 16 | + top = byte('9') |
| 17 | +) |
| 18 | + |
| 19 | +// Point represents a 2D coordinate. |
| 20 | +type Point struct { |
| 21 | + X, Y int |
| 22 | +} |
| 23 | + |
| 24 | +type Grid struct { |
| 25 | + data []byte |
| 26 | + width int |
| 27 | + height int |
| 28 | +} |
| 29 | + |
| 30 | +func parseGrid(data string) Grid { |
| 31 | + lines := strings.Split(strings.TrimSpace(data), "\n") |
| 32 | + height := len(lines) |
| 33 | + width := len(lines[0]) |
| 34 | + |
| 35 | + var gridData []byte |
| 36 | + for _, line := range lines { |
| 37 | + gridData = append(gridData, []byte(line)...) |
| 38 | + } |
| 39 | + |
| 40 | + return Grid{ |
| 41 | + data: gridData, |
| 42 | + width: width, |
| 43 | + height: height, |
| 44 | + } |
| 45 | +} |
| 46 | + |
| 47 | +func (g Grid) get(p Point) byte { |
| 48 | + if p.X < 0 || p.X >= g.width || p.Y < 0 || p.Y >= g.height { |
| 49 | + return 0 |
| 50 | + } |
| 51 | + return g.data[p.Y*g.width+p.X] |
| 52 | +} |
| 53 | + |
| 54 | +func (g Grid) neighbors(p Point) []Point { |
| 55 | + var neighbors []Point |
| 56 | + if p.Y > 0 { |
| 57 | + neighbors = append(neighbors, Point{X: p.X, Y: p.Y - 1}) // North |
| 58 | + } |
| 59 | + if p.X < g.width-1 { |
| 60 | + neighbors = append(neighbors, Point{X: p.X + 1, Y: p.Y}) // East |
| 61 | + } |
| 62 | + if p.Y < g.height-1 { |
| 63 | + neighbors = append(neighbors, Point{X: p.X, Y: p.Y + 1}) // South |
| 64 | + } |
| 65 | + if p.X > 0 { |
| 66 | + neighbors = append(neighbors, Point{X: p.X - 1, Y: p.Y}) // West |
| 67 | + } |
| 68 | + return neighbors |
| 69 | +} |
| 70 | + |
| 71 | +type queueItem struct { |
| 72 | + point Point |
| 73 | + height byte |
| 74 | +} |
| 75 | + |
| 76 | +func (g Grid) bfs(start Point) int { |
| 77 | + visited := make(map[Point]bool) |
| 78 | + height9 := make(map[Point]bool) |
| 79 | + queue := list.New() |
| 80 | + |
| 81 | + queue.PushBack(queueItem{start, bottom}) |
| 82 | + |
| 83 | + for queue.Len() > 0 { |
| 84 | + front := queue.Front() |
| 85 | + queue.Remove(front) |
| 86 | + item := front.Value.(queueItem) |
| 87 | + |
| 88 | + xy := item.point |
| 89 | + height := item.height |
| 90 | + |
| 91 | + visited[xy] = true |
| 92 | + |
| 93 | + if g.get(xy) == top { |
| 94 | + height9[xy] = true |
| 95 | + } |
| 96 | + |
| 97 | + for _, neigh := range g.neighbors(xy) { |
| 98 | + if g.get(neigh) == height+1 && !visited[neigh] { |
| 99 | + queue.PushBack(queueItem{neigh, height + 1}) |
| 100 | + } |
| 101 | + } |
| 102 | + } |
| 103 | + |
| 104 | + return len(height9) |
| 105 | +} |
| 106 | + |
| 107 | +func (g Grid) dfs(xy Point, height byte) int { |
| 108 | + if g.get(xy) == top { |
| 109 | + return 1 |
| 110 | + } |
| 111 | + |
| 112 | + sum := 0 |
| 113 | + for _, neigh := range g.neighbors(xy) { |
| 114 | + if g.get(neigh) == height+1 { |
| 115 | + sum += g.dfs(neigh, height+1) |
| 116 | + } |
| 117 | + } |
| 118 | + return sum |
| 119 | +} |
| 120 | + |
| 121 | +func part1(data string) int { |
| 122 | + grid := parseGrid(data) |
| 123 | + sum := 0 |
| 124 | + |
| 125 | + for y := 0; y < grid.height; y++ { |
| 126 | + for x := 0; x < grid.width; x++ { |
| 127 | + p := Point{X: x, Y: y} |
| 128 | + if grid.get(p) == bottom { |
| 129 | + sum += grid.bfs(p) |
| 130 | + } |
| 131 | + } |
| 132 | + } |
| 133 | + |
| 134 | + return sum |
| 135 | +} |
| 136 | + |
| 137 | +func part2(data string) int { |
| 138 | + grid := parseGrid(data) |
| 139 | + sum := 0 |
| 140 | + |
| 141 | + for y := 0; y < grid.height; y++ { |
| 142 | + for x := 0; x < grid.width; x++ { |
| 143 | + p := Point{X: x, Y: y} |
| 144 | + if grid.get(p) == bottom { |
| 145 | + sum += grid.dfs(p, bottom) |
| 146 | + } |
| 147 | + } |
| 148 | + } |
| 149 | + |
| 150 | + return sum |
| 151 | +} |
| 152 | + |
| 153 | +func solve(data []byte) (int, int) { |
| 154 | + input := string(data) |
| 155 | + return part1(input), part2(input) |
| 156 | +} |
| 157 | + |
| 158 | +func main() { |
| 159 | + filename := "input.txt" |
| 160 | + elapsed := false |
| 161 | + |
| 162 | + for i := 1; i < len(os.Args); i++ { |
| 163 | + arg := os.Args[i] |
| 164 | + if arg == "--elapsed" { |
| 165 | + elapsed = true |
| 166 | + } else if !strings.HasPrefix(arg, "-") { |
| 167 | + filename = arg |
| 168 | + } |
| 169 | + } |
| 170 | + |
| 171 | + data, err := os.ReadFile(filename) |
| 172 | + if err != nil { |
| 173 | + log.Fatal(err) |
| 174 | + } |
| 175 | + |
| 176 | + if elapsed { |
| 177 | + start := time.Now() |
| 178 | + result1, result2 := solve(data) |
| 179 | + duration := time.Since(start) |
| 180 | + |
| 181 | + fmt.Println(result1) |
| 182 | + fmt.Println(result2) |
| 183 | + fmt.Printf("elapsed: %f ms\n", duration.Seconds()*1000.0) |
| 184 | + } else { |
| 185 | + result1, result2 := solve(data) |
| 186 | + |
| 187 | + fmt.Println(result1) |
| 188 | + fmt.Println(result2) |
| 189 | + } |
| 190 | +} |
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