2025 day07

Author: liamgallear

2025/day07/.bench

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+{"Lines":[{"Name":"Part 1","N":1244,"NsPerOp":960015,"AllocedBytesPerOp":0,"AllocsPerOp":0,"MBPerS":0,"Measured":1,"Ord":0},{"Name":"Part 2","N":1171,"NsPerOp":1049460,"AllocedBytesPerOp":0,"AllocsPerOp":0,"MBPerS":0,"Measured":1,"Ord":0}],"Measured":1}

2025/day07/README.md

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+<!-- You can add some comments here if you want to :D -->

2025/day07/main.go

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+package main
+
+import (
+	_ "embed"
+	"os"
+)
+
+//go:embed input.txt
+var input string
+
+//go:embed input_test.txt
+var inputTest string
+
+func main() {
+	// Check argv if we use test input or not
+	if len(os.Args) > 1 && os.Args[1] == "test" {
+		input = inputTest
+	}
+
+	answer := doPartOne(input)
+	println(answer)
+
+	answer = doPartTwo(input)
+	println(answer)
+}

2025/day07/main_test.go

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+package main
+
+import "testing"
+
+func BenchmarkPartOne(b *testing.B) {
+	for n := 0; n < b.N; n++ {
+		doPartOne(input)
+	}
+}
+
+func BenchmarkPartTwo(b *testing.B) {
+	for n := 0; n < b.N; n++ {
+		doPartTwo(input)
+	}
+}

2025/day07/part1.go

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+package main
+
+import (
+	"image"
+	"strings"
+)
+
+func doPartOne(input string) int {
+	lines := strings.Split(strings.TrimSpace(input), "\n")
+	mapper, _, S := makeImagePointMapRect(lines)
+
+	// Pre-allocate with reasonable capacity
+	seen := make(map[image.Point]bool, len(lines)*len(lines[0])/4)
+	queue := make([]image.Point, 0, 256)
+	queue = append(queue, S)
+	ans := 0
+	head := 0
+
+	for head < len(queue) {
+		P := queue[head]
+		head++
+
+		if seen[P] {
+			continue
+		}
+		seen[P] = true
+
+		np := P.Add(image.Point{0, 1})
+		val, ok := mapper[np]
+		if !ok {
+			continue
+		}
+
+		if val != '^' {
+			queue = append(queue, np)
+			continue
+		}
+
+		ans++
+		queue = append(queue, np.Add(image.Point{-1, 0}), np.Add(image.Point{1, 0}))
+	}
+
+	return ans
+}
+
+func makeImagePointMapRect(lines []string) (mapping map[image.Point]rune, rect image.Rectangle, S image.Point) {
+	mapping = make(map[image.Point]rune)
+	for y, s := range lines {
+		for x, r := range s {
+			mapping[image.Point{x, y}] = r
+			if r == 'S' {
+				S = image.Point{x, y}
+			}
+		}
+	}
+	rect = image.Rect(0, 0, len(lines[0]), len(lines))
+	return
+}

2025/day07/part2.go

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+package main
+
+import (
+	"image"
+	"strings"
+)
+
+type MapRect struct {
+	m     map[image.Point]rune
+	r     image.Rectangle
+	cache map[image.Point]int
+}
+
+func doPartTwo(input string) int {
+	lines := strings.Split(strings.TrimSpace(input), "\n")
+	mapper, rect, S := makeImagePointMapRect(lines)
+	m := MapRect{
+		m:     mapper,
+		r:     rect,
+		cache: make(map[image.Point]int),
+	}
+
+	return m.score(S)
+}
+
+func (m MapRect) score(i image.Point) int {
+	// Check cache first
+	if val, ok := m.cache[i]; ok {
+		return val
+	}
+
+	np := i.Add(image.Point{0, 1})
+	if !np.In(m.r) {
+		m.cache[i] = 1
+		return 1
+	}
+
+	var result int
+	if m.m[np] == '^' {
+		result = m.score(np.Add(image.Point{-1, 0})) + m.score(np.Add(image.Point{1, 0}))
+	} else {
+		result = m.score(np)
+	}
+
+	m.cache[i] = result
+	return result
+}