Day09

2024/gareth/day09/day09.go

@@ -0,0 +1,104 @@
+package day09
+
+func Part1(input string) int {
+	files, gaps, lengthOfFinalFile := parseInput(input)
+	checksum := compactFiles(files, gaps, lengthOfFinalFile)
+	return checksum
+}
+
+func Part2(input string) int {
+	files, freeSpaces := parseInputPart2(input)
+	checksum := calculateChecksum(files, freeSpaces)
+	return checksum
+}
+
+func parseInput(input string) ([]int, []int, int) {
+	var files []int
+	var gaps []int
+	lengthOfFinalFile := 0
+	for i, char := range input {
+		if i%2 == 0 {
+			files = append(files, int(char-'0'))
+			lengthOfFinalFile += int(char - '0')
+		} else {
+			gaps = append(gaps, int(char-'0'))
+		}
+	}
+	return files, gaps, lengthOfFinalFile
+}
+
+func parseInputPart2(input string) ([][]int, [][]int) {
+	files, freeSpaces, position := [][]int{}, [][]int{}, 0
+	for index, char := range input {
+		length := int(char - '0')
+		if index%2 == 0 {
+			files = append(files, generateRange(position, position+length))
+		} else {
+			freeSpaces = append(freeSpaces, generateRange(position, position+length))
+		}
+		position += length
+	}
+	return files, freeSpaces
+}
+
+func compactFiles(files []int, gaps []int, lengthOfFinalFile int) int {
+	fileIndex := len(files) - 1
+	gapIndex := 0
+	position := files[0]
+	checksum := 0
+	fileID := files[0]
+
+	for lengthOfFinalFile != position {
+		// If there's a gap and a file to move then move the file
+		if gaps[gapIndex] > 0 && files[fileIndex] > 0 {
+			files[fileIndex]--
+			gaps[gapIndex]--
+			checksum += fileIndex * position
+			position++
+		}
+
+		// If this file is fully moved go to next file
+		if files[fileIndex] == 0 {
+			fileIndex--
+			fileID++
+		}
+
+		// Update gapIndex if this gap is filled
+		if gaps[gapIndex] == 0 {
+			gapIndex++
+			for f := 0; f < files[gapIndex]; f++ {
+				checksum += gapIndex * position
+				position++
+			}
+		}
+	}
+
+	return checksum
+}
+
+func generateRange(start, end int) []int {
+	rangeList := make([]int, end-start)
+	for i := range rangeList {
+		rangeList[i] = start + i
+	}
+	return rangeList
+}
+
+func calculateChecksum(files, freeSpaces [][]int) int {
+	checksum := 0
+	for fileIndex := len(files) - 1; fileIndex >= 0; fileIndex-- {
+		for spaceIndex := 0; spaceIndex < len(freeSpaces); spaceIndex++ {
+			if len(freeSpaces[spaceIndex]) >= len(files[fileIndex]) && files[fileIndex][0] > freeSpaces[spaceIndex][0] {
+				files[fileIndex] = freeSpaces[spaceIndex][:len(files[fileIndex])]
+				freeSpaces[spaceIndex] = freeSpaces[spaceIndex][len(files[fileIndex]):]
+			}
+		}
+	}
+
+	for fileID, file := range files {
+		for _, block := range file {
+			checksum += fileID * block
+		}
+	}
+	return checksum
+}

2024/gareth/day09/day09_test.go

@@ -0,0 +1,22 @@
+package day09
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestPart1(t *testing.T) {
+	r := Part1(`12345`)
+	assert.Equal(t, 60, r)
+}
+
+func TestPart1Long(t *testing.T) {
+	r := Part1(`2333133121414131402`)
+	assert.Equal(t, 1928, r)
+}
+
+func TestPart2(t *testing.T) {
+	r := Part2(`2333133121414131402`)
+	assert.Equal(t, 2858, r)
+}

2024/gareth/main.go

@@ -1,7 +1,7 @@
 package main
 
 import (
-	"aoc2024/day08"
+	"aoc2024/day09"
 	"fmt"
 	"os"
 	"time"
@@ -9,9 +9,11 @@ import (
 
 func main() {
 	start := time.Now()
-	data, _ := os.ReadFile("day08/input.txt")
-	fmt.Printf("part 1: %d\n", day08.Part1(string(data)))
-	fmt.Printf("part 2: %d\n", day08.Part2(string(data)))
+	data, _ := os.ReadFile("day09/input.txt")
+	fmt.Printf("part 1: %d\n", day09.Part1(string(data)))
+	fmt.Printf("part 2: %d\n", day09.Part2(string(data)))
 	elapsed := time.Since(start)
 	fmt.Printf("Execution time: %s\n", elapsed)
 }
+
+// 6320029754031