feat(2025): add day 7

Author: believer

go/2025/README.md

@@ -24,6 +24,7 @@ Collect stars by solving puzzles. Two puzzles will be made available on each day
 | [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 |
 
 ## Benchmarks
 
@@ -37,6 +38,7 @@ Using Go's built-in benchmarking with the [testing](https://pkg.go.dev/testing#h
 | 4   |   214451 |   5483916 |                      |
 | 5   |   116258 |     68155 | `96,29%` / -         |
 | 6   |   149919 |    986335 | `30,99%` / -         |
+| 7   |   671799 |    508323 |                      |
 
 All values are ns/op. \* compared to first solution.
 

go/2025/puzzles/day07/main.go

@@ -0,0 +1,95 @@
+package main
+
+import (
+	"fmt"
+
+	"github.com/believer/aoc-utils/files"
+	"github.com/believer/aoc-utils/grid"
+)
+
+// I spent too much time trying to make a flawed solution work.
+// I thought of BFS (I've had it in the back of my mind that
+// it would appear at some point) but kept working on the path I had taken ':D
+// Eventually, I gave up and looked at my solution from day 18 2024 to remember.
+
+func main() {
+	fmt.Println("Part 1: ", part1("input.txt"))
+	fmt.Println("Part 2: ", part2("input.txt"))
+}
+
+func part1(name string) (splits int) {
+	lines := files.ReadLines(name)
+	manifold := grid.New(lines)
+	start, _ := manifold.Find('S')
+
+	queue := []grid.Point{start}
+	seen := map[grid.Point]bool{}
+
+	for len(queue) > 0 {
+		beam := queue[0]
+		queue = queue[1:]
+
+		// Keep track of what we've seen since beams
+		// can split into the same position
+		if _, ok := seen[beam]; ok {
+			continue
+		}
+
+		if !manifold.InBounds(beam) {
+			continue
+		}
+
+		seen[beam] = true
+
+		if manifold.Get(beam) == '^' {
+			splits += 1
+			leftSplit := beam.Add(grid.LEFT)
+			rightSplit := beam.Add(grid.RIGHT)
+
+			queue = append(queue, leftSplit)
+			queue = append(queue, rightSplit)
+		} else {
+			queue = append(queue, beam.Add(grid.DOWN))
+		}
+	}
+
+	return
+}
+
+// Another thing I've had in mind would show up is Dynamic Programming (DP) which
+// I first learnt about in 2023 day 12. Essentially, it's taking a problem and breaking
+// it down into smaller subproblems and recursively solving them.
+//
+// I solved it without a seen cache first, which worked for the example, but it was
+// immediately clear that didn't work for the real input. A simple change and it worked.
+func part2(name string) int {
+	lines := files.ReadLines(name)
+	manifold := grid.New(lines)
+	start, _ := manifold.Find('S')
+	seen := map[grid.Point]int{}
+
+	return timelines(manifold, start, seen)
+}
+
+func timelines(g grid.Grid, point grid.Point, seen map[grid.Point]int) int {
+	if v, ok := seen[point]; ok {
+		return v
+	}
+
+	if !g.InBounds(point) {
+		return 1
+	}
+
+	if g.Get(point) == '^' {
+		leftSplit := point.Add(grid.LEFT)
+		rightSplit := point.Add(grid.RIGHT)
+
+		return timelines(g, leftSplit, seen) + timelines(g, rightSplit, seen)
+	}
+
+	down := point.Add(grid.DOWN)
+	result := timelines(g, down, seen)
+	seen[down] = result
+
+	return result
+}

go/2025/puzzles/day07/main_test.go

@@ -0,0 +1,35 @@
+package main
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestPart1(t *testing.T) {
+	t.Run("Part 1", func(t *testing.T) {
+		expected := 21
+		actual := part1("test-input.txt")
+		assert.Equal(t, expected, actual)
+	})
+}
+
+func TestPart2(t *testing.T) {
+	t.Run("Part 2", func(t *testing.T) {
+		expected := 40
+		actual := part2("test-input.txt")
+		assert.Equal(t, expected, actual)
+	})
+}
+
+func BenchmarkPart1(b *testing.B) {
+	for b.Loop() {
+		part1("input.txt")
+	}
+}
+
+func BenchmarkPart2(b *testing.B) {
+	for b.Loop() {
+		part2("input.txt")
+	}
+}

go/2025/puzzles/day07/test-input.txt

@@ -0,0 +1,16 @@
+.......S.......
+...............
+.......^.......
+...............
+......^.^......
+...............
+.....^.^.^.....
+...............
+....^.^...^....
+...............
+...^.^...^.^...
+...............
+..^...^.....^..
+...............
+.^.^.^.^.^...^.
+...............