feat(2024): add day 12

go/2024/README.md

@@ -25,6 +25,7 @@ Collect stars by solving puzzles. Two puzzles will be made available on each day
 | [Day 9: Disk Fragmenter](https://github.com/believer/advent-of-code/blob/master/go/2024/puzzles/day09/main.go)       | 🌟  | 6384282079460 | 🌟  |   6408966547049 |
 | [Day 10: Hoof It](https://github.com/believer/advent-of-code/blob/master/go/2024/puzzles/day10/main.go)              | 🌟  |           652 | 🌟  |            1432 |
 | [Day 11: Plutonian Pebbles](https://github.com/believer/advent-of-code/blob/master/go/2024/puzzles/day11/main.go)    | 🌟  |        187738 | 🌟  | 223767210249237 |
+| [Day 12: Garden Groups](https://github.com/believer/advent-of-code/blob/master/go/2024/puzzles/day12/main.go)        | 🌟  |       1522850 | 🌟  |          953738 |
 
 ## Benchmarks
 
@@ -43,6 +44,7 @@ Using Go's built-in benchmarking with the [testing](https://pkg.go.dev/testing#h
 | 9   | 381476181 ns/op |  171042257 ns/op |                     |
 | 10  |   1424599 ns/op |    1789071 ns/op |                     |
 | 11  |    424021 ns/op |   15488584 ns/op |                     |
+| 12  |  10984420 ns/op |   16856988 ns/op |                     |
 
 \* compared to first solution
 

go/2024/puzzles/day12/main.go

@@ -0,0 +1,158 @@
+package main
+
+import (
+	"fmt"
+
+	"github.com/believer/aoc-2024/utils/files"
+)
+
+// BFS to find plant regions and perimeters
+// For part 2 find corners of areas which show how many sides it has
+func main() {
+	fmt.Println("Part 1: ", part1("input.txt"))
+	fmt.Println("Part 2: ", part2("input.txt"))
+}
+
+type Location struct {
+	r, c int
+}
+
+var directions = [][]int{
+	{-1, 0}, // Above
+	{0, 1},  // Right
+	{1, 0},  // Below
+	{0, -1}, // Left
+}
+
+func part1(name string) int {
+	plants := files.ReadLines(name)
+	grid := map[Location]byte{}
+	visited := map[Location]bool{}
+
+	rows := len(plants)
+	cols := len(plants[0])
+	price := 0
+
+	for r := range rows {
+		for c := range cols {
+			grid[Location{r, c}] = plants[r][c]
+		}
+	}
+
+	for r := range rows {
+		for c := range cols {
+			area, perimeter := findPlantBed(grid, visited, Location{r, c})
+			price += len(area) * perimeter
+		}
+	}
+
+	return price
+}
+
+func part2(name string) int {
+	plants := files.ReadLines(name)
+	grid := map[Location]byte{}
+	visited := map[Location]bool{}
+
+	rows := len(plants)
+	cols := len(plants[0])
+	price := 0
+
+	for r := range rows {
+		for c := range cols {
+			grid[Location{r, c}] = plants[r][c]
+		}
+	}
+
+	for r := range rows {
+		for c := range cols {
+			area, _ := findPlantBed(grid, visited, Location{r, c})
+			price += len(area) * findCorners(area)
+		}
+	}
+
+	return price
+}
+
+// The number of corners shows how many sides we have
+func findCorners(area map[Location]bool) int {
+	corners := 0
+
+	cornerChecks := []struct {
+		offsets        []Location
+		requiredStates []bool
+	}{
+		// Outer corners
+		{[]Location{{0, -1}, {-1, 0}}, []bool{false, false}}, // Top left
+		{[]Location{{0, 1}, {-1, 0}}, []bool{false, false}},  // Top right
+		{[]Location{{0, -1}, {1, 0}}, []bool{false, false}},  // Bottom left
+		{[]Location{{0, 1}, {1, 0}}, []bool{false, false}},   // Bottom right
+
+		// Inner corners
+		{[]Location{{-1, -1}, {-1, 0}, {0, -1}}, []bool{false, true, true}}, // Inside top left
+		{[]Location{{-1, 1}, {-1, 0}, {0, 1}}, []bool{false, true, true}},   // Inside top right
+		{[]Location{{1, -1}, {1, 0}, {0, -1}}, []bool{false, true, true}},   // Inside bottom left
+		{[]Location{{1, 1}, {1, 0}, {0, 1}}, []bool{false, true, true}},     // Inside bottom right
+	}
+
+	for a := range area {
+		for _, check := range cornerChecks {
+			match := true
+
+			for i, offset := range check.offsets {
+				neighbor := Location{a.r + offset.r, a.c + offset.c}
+
+				if _, ok := area[neighbor]; ok != check.requiredStates[i] {
+					match = false
+					break
+				}
+			}
+
+			if match {
+				corners++
+			}
+		}
+	}
+
+	return corners
+}
+
+func findPlantBed(grid map[Location]byte, visited map[Location]bool, start Location) (map[Location]bool, int) {
+	queue := []Location{start}
+	perimeter := 0
+	area := map[Location]bool{}
+
+	for len(queue) > 0 {
+		current := queue[0]
+		queue = queue[1:]
+
+		if _, ok := visited[current]; ok {
+			continue
+		}
+
+		neighbors := getNeighbors(grid, current)
+		perimeter += 4 - len(neighbors)
+		area[current] = true
+		visited[current] = true
+
+		for _, neighbor := range neighbors {
+			queue = append(queue, neighbor)
+		}
+	}
+
+	return area, perimeter
+}
+
+func getNeighbors(grid map[Location]byte, current Location) []Location {
+	neighbors := []Location{}
+
+	for _, d := range directions {
+		next := Location{current.r + d[0], current.c + d[1]}
+
+		if value, ok := grid[next]; ok && value == grid[current] {
+			neighbors = append(neighbors, next)
+		}
+	}
+
+	return neighbors
+}

go/2024/puzzles/day12/main_test.go

@@ -0,0 +1,51 @@
+package main
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestPart1(t *testing.T) {
+	t.Run("Part 1", func(t *testing.T) {
+		expected := 140
+		actual := part1("test-input.txt")
+		assert.Equal(t, expected, actual)
+	})
+}
+
+func TestPart1Medium(t *testing.T) {
+	t.Run("Part 1", func(t *testing.T) {
+		expected := 772
+		actual := part1("test-input-medium.txt")
+		assert.Equal(t, expected, actual)
+	})
+}
+
+func TestPart1Large(t *testing.T) {
+	t.Run("Part 1", func(t *testing.T) {
+		expected := 1930
+		actual := part1("test-input-large.txt")
+		assert.Equal(t, expected, actual)
+	})
+}
+
+func TestPart2(t *testing.T) {
+	t.Run("Part 2", func(t *testing.T) {
+		expected := 80
+		actual := part2("test-input.txt")
+		assert.Equal(t, expected, actual)
+	})
+}
+
+func BenchmarkPart1(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		part1("input.txt")
+	}
+}
+
+func BenchmarkPart2(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		part2("input.txt")
+	}
+}

go/2024/puzzles/day12/test-input-large.txt

@@ -0,0 +1,10 @@
+RRRRIICCFF
+RRRRIICCCF
+VVRRRCCFFF
+VVRCCCJFFF
+VVVVCJJCFE
+VVIVCCJJEE
+VVIIICJJEE
+MIIIIIJJEE
+MIIISIJEEE
+MMMISSJEEE

go/2024/puzzles/day12/test-input-medium.txt

@@ -0,0 +1,5 @@
+OOOOO
+OXOXO
+OOOOO
+OXOXO
+OOOOO

go/2024/puzzles/day12/test-input.txt

@@ -0,0 +1,4 @@
+AAAA
+BBCD
+BBCC
+EEEC