Solve 2024 day 9 in go

2024/go/day-09/main.go

@@ -0,0 +1,154 @@
+package main
+
+import (
+	"fmt"
+	"log"
+	"os"
+	"slices"
+	"strings"
+)
+
+func readInput() (fileMap []int, err error) {
+	content, err := os.ReadFile("input")
+	if err != nil {
+		return
+	}
+
+	line := strings.TrimSpace(string(content))
+	for _, digit := range line {
+		fileMap = append(fileMap, int(digit-'0'))
+	}
+
+	return
+}
+
+func convertToBlockMap(fileMap []int) []int {
+	var blockMap []int
+
+	for i, digit := range fileMap {
+		for _ = range digit {
+			if i%2 == 0 { // Even
+				blockMap = append(blockMap, i/2)
+			} else { // Odd
+				blockMap = append(blockMap, -1)
+			}
+		}
+	}
+
+	return blockMap
+}
+
+func compress1(blockMap []int) []int {
+	newBlockMap := make([]int, len(blockMap))
+	copy(newBlockMap, blockMap)
+
+	leftIndex := 0
+	rightIndex := len(newBlockMap) - 1
+
+	for leftIndex < rightIndex {
+		left := &newBlockMap[leftIndex]
+		right := &newBlockMap[rightIndex]
+
+		if *left == -1 && *right != -1 {
+			*left, *right = *right, *left
+
+			leftIndex++
+			rightIndex--
+
+			continue
+		}
+
+		if *left != -1 {
+			leftIndex++
+		}
+		if *right == -1 {
+			rightIndex--
+		}
+	}
+
+	return newBlockMap
+}
+
+type segment struct {
+	index, length int
+}
+
+func getSegments(fileMap []int) (files, freeSpaces []segment) {
+	var blockIndex int
+
+	for segmentIndex, length := range fileMap {
+		if segmentIndex%2 == 0 { // Even
+			files = append(files, segment{blockIndex, length})
+		} else { // Odd
+			freeSpaces = append(freeSpaces, segment{blockIndex, length})
+		}
+
+		blockIndex += length
+	}
+
+	slices.Reverse(files)
+
+	return
+}
+
+func compress2(blockMap, fileMap []int) []int {
+	newBlockMap := make([]int, len(blockMap))
+	copy(newBlockMap, blockMap)
+
+	files, freeSpaces := getSegments(fileMap)
+
+	for fileIndex, file := range files {
+		for freeSpaceIndex, freeSpace := range freeSpaces {
+			if freeSpace.index > file.index {
+				break
+			}
+
+			if freeSpace.length >= file.length {
+				// Swap blocks
+				idNumber := newBlockMap[file.index]
+				for i := 0; i < file.length; i++ {
+					newBlockMap[freeSpaces[freeSpaceIndex].index+i] = idNumber
+					newBlockMap[files[fileIndex].index+i] = -1
+				}
+
+				// Shrink free space
+				freeSpaces[freeSpaceIndex].index += file.length
+				freeSpaces[freeSpaceIndex].length -= file.length
+
+				break
+			}
+		}
+	}
+
+	return newBlockMap
+}
+
+func calculateChecksum(fileMap []int) int {
+	var sum int
+
+	for i, num := range fileMap {
+		if num == -1 {
+			continue
+		}
+
+		sum += i * num
+	}
+
+	return sum
+}
+
+func main() {
+	fileMap, err := readInput()
+	if err != nil {
+		log.Fatalln(err)
+	}
+
+	blockMap := convertToBlockMap(fileMap)
+	checksum1 := calculateChecksum(compress1(blockMap))
+	checksum2 := calculateChecksum(compress2(blockMap, fileMap))
+
+	// Part one
+	fmt.Println("Checksum 1:", checksum1)
+	// Part two
+	fmt.Println("Checksum 2:", checksum2)
+}