Day 09.

day_09/data.txt

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day_09/example_data.txt

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+2333133121414131402

day_09/solution.go

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+package day_09
+
+const Empty = -1
+
+type State int
+
+type Chunk struct {
+	start, length int
+}
+
+const (
+	ReadingValue = iota
+	ReadingSpace = iota
+)
+
+// task:https://adventofcode.com/2024/day/9
+func SolveBasic(input string) int {
+	diagram := loadDiagram(input)
+
+	diagram = compress(diagram)
+
+	return hashSum(diagram)
+}
+
+// task:https://adventofcode.com/2024/day/9#part2
+func SolveComplex(input string) int {
+	diagram := loadDiagram(input)
+
+	diagram = safeCompress(diagram)
+
+	return hashSum(diagram)
+}
+
+func hashSum(diagram []int) int {
+	sum := 0
+	for i, val := range diagram {
+		if val != Empty {
+			sum += i * val
+		}
+	}
+	return sum
+}
+
+func compress(diagram []int) []int {
+	startingCursor := 0
+	endingCursor := len(diagram) - 1
+
+	for {
+		for diagram[startingCursor] != Empty && startingCursor < endingCursor {
+			startingCursor++
+		}
+		for diagram[endingCursor] == Empty && startingCursor < endingCursor {
+			endingCursor--
+		}
+		if startingCursor >= endingCursor {
+			break
+		}
+		diagram[startingCursor] = diagram[endingCursor]
+		diagram[endingCursor] = Empty
+	}
+	return diagram
+}
+
+func safeCompress(diagram []int) []int {
+	value := diagram[len(diagram)-1]
+
+	for value >= 0 {
+		file := locateFile(diagram, value)
+		if hole, found := findHole(diagram, file.start, file.length); found {
+			copyFile(diagram, file, value, hole)
+		}
+		value--
+	}
+
+	return diagram
+}
+
+func copyFile(diagram []int, file Chunk, value int, hole Chunk) {
+	for i := 0; i < file.length; i++ {
+		diagram[hole.start+i] = value
+		diagram[file.start+i] = Empty
+	}
+}
+
+func findHole(diagram []int, end int, length int) (Chunk, bool) {
+	for i := 0; i < end; i++ {
+		if diagram[i] == Empty {
+			size := 0
+			for i+size < end && diagram[i+size] == Empty {
+				size++
+			}
+			if size >= length {
+				return Chunk{i, size}, true
+			}
+		}
+	}
+	return Chunk{}, false
+}
+
+func locateFile(diagram []int, value int) Chunk {
+	length := 0
+	for i := 0; i < len(diagram); i++ {
+		if diagram[i] == value {
+			start := i
+			for i+length < len(diagram) && diagram[i+length] == value {
+				length++
+			}
+			return Chunk{start, length}
+		}
+	}
+	panic("couldn't find the value")
+}
+
+func loadDiagram(input string) []int {
+	diagram := make([]int, 0, len(input)*5) // we reserve about the average we need
+	state := ReadingValue
+	currentValue := 0
+
+	for _, r := range input {
+		lenght := int(r - '0')
+		if state == ReadingValue {
+			for i := 0; i < lenght; i++ {
+				diagram = append(diagram, currentValue)
+			}
+			currentValue++
+		} else {
+			for i := 0; i < lenght; i++ {
+				diagram = append(diagram, Empty)
+			}
+		}
+		state = (state + 1) % 2
+	}
+
+	return diagram
+}

day_09/solution_test.go

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+package day_09_test
+
+import (
+	"advent_of_code_2024/day_09"
+	_ "embed"
+	"testing"
+)
+
+//go:embed example_data.txt
+var ExampleData string
+
+func TestBasicSolutionExample(t *testing.T) {
+	result := day_09.SolveBasic(ExampleData)
+	if result != 1928 {
+		t.Fatalf("Expected 1928 received %d", result)
+	}
+}
+
+func TestComplexSolutionExample(t *testing.T) {
+	result := day_09.SolveComplex(ExampleData)
+	if result != 2858 {
+		t.Fatalf("Expected 2858 received %d", result)
+	}
+}