feat(2025): add day 12

Author: believer

go/2025/README.md

@@ -16,19 +16,20 @@ Collect stars by solving puzzles. Two puzzles will be made available on each day
 
 ## Days
 
-| Day                                                                                                                | #1  |     #1 Answer | #2  |       #2 Answer |
-| ------------------------------------------------------------------------------------------------------------------ | --- | ------------: | --- | --------------: |
-| [Day 1: Secret Entrance](https://github.com/believer/advent-of-code/blob/master/go/2025/puzzles/day01/main.go)     | 🌟  |           997 | 🌟  |            5978 |
-| [Day 2: Gift Shop](https://github.com/believer/advent-of-code/blob/master/go/2025/puzzles/day02/main.go)           | 🌟  |    9188031749 | 🌟  |     11323661261 |
-| [Day 3: Lobby](https://github.com/believer/advent-of-code/blob/master/go/2025/puzzles/day03/main.go)               | 🌟  |         16993 | 🌟  | 168617068915447 |
-| [Day 4: Printing Department](https://github.com/believer/advent-of-code/blob/master/go/2025/puzzles/day04/main.go) | 🌟  |          1320 | 🌟  |            8354 |
-| [Day 5: Cafeteria](https://github.com/believer/advent-of-code/blob/master/go/2025/puzzles/day05/main.go)           | 🌟  |           885 | 🌟  | 348115621205535 |
-| [Day 6: Trash Compactor](https://github.com/believer/advent-of-code/blob/master/go/2025/puzzles/day06/main.go)     | 🌟  | 6209956042374 | 🌟  |  12608160008022 |
-| [Day 7: Laboratories](https://github.com/believer/advent-of-code/blob/master/go/2025/puzzles/day07/main.go)        | 🌟  |          1711 | 🌟  |  36706966158365 |
-| [Day 8: Playground](https://github.com/believer/advent-of-code/blob/master/go/2025/puzzles/day08/main.go)          | 🌟  |         69192 | 🌟  |      7264308110 |
-| [Day 9: Movie Theater](https://github.com/believer/advent-of-code/blob/master/go/2025/puzzles/day09/main.go)       | 🌟  |    4772103936 | 🌟  |      1529675217 |
-| [Day 10: Factory](https://github.com/believer/advent-of-code/blob/master/go/2025/puzzles/day10/main.go)            | 🌟  |           455 |     |                 |
-| [Day 11: Reactor](https://github.com/believer/advent-of-code/blob/master/go/2025/puzzles/day11/main.go)            | 🌟  |           431 | 🌟  | 358458157650450 |
+| Day                                                                                                                 | #1  |     #1 Answer | #2  |       #2 Answer |
+| ------------------------------------------------------------------------------------------------------------------- | --- | ------------: | --- | --------------: |
+| [Day 1: Secret Entrance](https://github.com/believer/advent-of-code/blob/master/go/2025/puzzles/day01/main.go)      | 🌟  |           997 | 🌟  |            5978 |
+| [Day 2: Gift Shop](https://github.com/believer/advent-of-code/blob/master/go/2025/puzzles/day02/main.go)            | 🌟  |    9188031749 | 🌟  |     11323661261 |
+| [Day 3: Lobby](https://github.com/believer/advent-of-code/blob/master/go/2025/puzzles/day03/main.go)                | 🌟  |         16993 | 🌟  | 168617068915447 |
+| [Day 4: Printing Department](https://github.com/believer/advent-of-code/blob/master/go/2025/puzzles/day04/main.go)  | 🌟  |          1320 | 🌟  |            8354 |
+| [Day 5: Cafeteria](https://github.com/believer/advent-of-code/blob/master/go/2025/puzzles/day05/main.go)            | 🌟  |           885 | 🌟  | 348115621205535 |
+| [Day 6: Trash Compactor](https://github.com/believer/advent-of-code/blob/master/go/2025/puzzles/day06/main.go)      | 🌟  | 6209956042374 | 🌟  |  12608160008022 |
+| [Day 7: Laboratories](https://github.com/believer/advent-of-code/blob/master/go/2025/puzzles/day07/main.go)         | 🌟  |          1711 | 🌟  |  36706966158365 |
+| [Day 8: Playground](https://github.com/believer/advent-of-code/blob/master/go/2025/puzzles/day08/main.go)           | 🌟  |         69192 | 🌟  |      7264308110 |
+| [Day 9: Movie Theater](https://github.com/believer/advent-of-code/blob/master/go/2025/puzzles/day09/main.go)        | 🌟  |    4772103936 | 🌟  |      1529675217 |
+| [Day 10: Factory](https://github.com/believer/advent-of-code/blob/master/go/2025/puzzles/day10/main.go)             | 🌟  |           455 |     |                 |
+| [Day 11: Reactor](https://github.com/believer/advent-of-code/blob/master/go/2025/puzzles/day11/main.go)             | 🌟  |           431 | 🌟  | 358458157650450 |
+| [Day 12: Christmas Tree Farm](https://github.com/believer/advent-of-code/blob/master/go/2025/puzzles/day12/main.go) | 🌟  |           422 |     |                 |
 
 ## Benchmarks
 
@@ -47,6 +48,7 @@ Using Go's built-in benchmarking with the [testing](https://pkg.go.dev/testing#h
 | 9   |    593637 | 375621306 | - / `90,43%`         |
 | 10  | 256756802 |         - |                      |
 | 11  |    106015 |    311170 |                      |
+| 12  |    274895 |         - |                      |
 
 All values are ns/op. \* compared to first solution.
 

go/2025/puzzles/day12/main.go

@@ -0,0 +1,87 @@
+package main
+
+import (
+	"fmt"
+	"strings"
+
+	"github.com/believer/aoc-utils/files"
+	"github.com/believer/aoc-utils/utils"
+)
+
+// A bit troll-y :D From reading I thought it was going to be
+// impossible. But, I started parsing the list and tried if the
+// area would actually fit the size of the shapes and it worked!
+
+func main() {
+	fmt.Println("Part 1: ", part1("input.txt"))
+}
+
+type Region struct {
+	width, height int
+	counts        []int
+}
+
+func (r *Region) Area() int {
+	return r.width * r.height
+}
+
+func part1(name string) (fits int) {
+	paragraphs := files.ReadParagraphs(name)
+
+	// Get size of packages
+	shapes := []int{}
+
+	for _, p := range paragraphs[:6] {
+		shape := 0
+
+		for _, s := range p[1:] {
+			for v := range strings.SplitSeq(s, "") {
+				if v == "#" {
+					shape++
+				}
+			}
+		}
+
+		shapes = append(shapes, shape)
+	}
+
+	// Get region sizes and number of packages
+	packages := [][]int{}
+	var regions []Region
+
+	for _, p := range paragraphs[6:] {
+		for _, s := range p {
+			counts := []int{}
+			region := strings.Fields(s)
+			area := strings.Split(region[0][:len(region[0])-1], "x")
+
+			for _, r := range region[1:] {
+				counts = append(counts, utils.MustIntFromString(r))
+			}
+
+			packages = append(packages, counts)
+
+			regions = append(regions, Region{
+				height: utils.MustIntFromString(area[0]),
+				width:  utils.MustIntFromString(area[1]),
+				counts: counts,
+			})
+		}
+	}
+
+	// Check if package sizes will fit inside the area
+	for i, r := range regions {
+		p := packages[i]
+		size := 0
+
+		for i, pp := range p {
+			size += shapes[i] * pp
+		}
+
+		if r.Area() >= size {
+			fits++
+		}
+	}
+
+	return
+}

go/2025/puzzles/day12/main_test.go

@@ -0,0 +1,21 @@
+package main
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestPart1(t *testing.T) {
+	t.Run("Part 1", func(t *testing.T) {
+		expected := 3
+		actual := part1("test-input.txt")
+		assert.Equal(t, expected, actual)
+	})
+}
+
+func BenchmarkPart1(b *testing.B) {
+	for b.Loop() {
+		part1("input.txt")
+	}
+}

go/2025/puzzles/day12/test-input.txt

@@ -0,0 +1,33 @@
+0:
+###
+##.
+##.
+
+1:
+###
+##.
+.##
+
+2:
+.##
+###
+##.
+
+3:
+##.
+###
+##.
+
+4:
+###
+#..
+###
+
+5:
+###
+.#.
+###
+
+4x4: 0 0 0 0 2 0
+12x5: 1 0 1 0 2 2
+12x5: 1 0 1 0 3 2