Task 9 completed

No bruteforce necessary, lets go

day9/main.go

@@ -0,0 +1,183 @@
+package main
+
+import (
+	"fmt"
+	"slices"
+	"strconv"
+	"unicode"
+
+	"git.mstar.dev/mstar/aoc24/util"
+	"git.mstar.dev/mstar/goutils/other"
+	"git.mstar.dev/mstar/goutils/sliceutils"
+)
+
+const EmptyBlockId = -1
+
+func findFirstEmptyIndex(list []int) (int, bool) {
+	for i, v := range list {
+		if v == EmptyBlockId {
+			return i, true
+		}
+	}
+	return -1, false
+}
+
+func findLastUsedIndex(list []int) (int, bool) {
+	for i := len(list) - 1; i >= 0; i-- {
+		if list[i] != EmptyBlockId {
+			return i, true
+		}
+	}
+	return -1, false
+}
+
+func indicesToBlocks(indices []int) []int {
+	blocks := []int{}
+	// indices are len of block, len of empty, len of block, len of empty
+	isFile := true
+	// block id increments each time a block with a file completes
+	i := 0
+	for _, size := range indices {
+		// Write the full block
+		for range size {
+			if isFile {
+				blocks = append(blocks, i)
+			} else {
+				blocks = append(blocks, EmptyBlockId)
+			}
+		}
+		// If current block is a file, increment id counter
+		if isFile {
+			i++
+		}
+		// Swap state
+		isFile = !isFile
+	}
+	return blocks
+}
+
+func compactBlocks1(blocks []int) (compacted []int) {
+	compacted = slices.Clone(blocks)
+
+	firstEmpty, _ := findFirstEmptyIndex(compacted)
+	lastUsed, _ := findLastUsedIndex(compacted)
+	for firstEmpty < lastUsed {
+		util.SliceSwap(compacted, firstEmpty, lastUsed)
+		firstEmpty, _ = findFirstEmptyIndex(compacted)
+		lastUsed, _ = findLastUsedIndex(compacted)
+	}
+
+	return
+}
+
+func checksumBlocks(blocks []int) uint64 {
+	var total uint64 = 0
+	for i, v := range blocks {
+		if v == EmptyBlockId {
+			continue
+		}
+		total += uint64(i * v)
+	}
+	return total
+}
+
+func findFirstEmptyBlockOfLength(list []int, length int) (int, bool) {
+	lenCounter := 0
+	for i, v := range list {
+		if v == EmptyBlockId {
+			lenCounter++
+		} else {
+			lenCounter = 0
+		}
+		if lenCounter == length {
+			// Start of empty block with (at least) target length is at i - (lenCounter-1), since lenCounter starts at 0
+			return i - lenCounter + 1, true
+		}
+	}
+	return -1, false
+}
+
+func findBlockById(list []int, blockId int) (start, length int, found bool) {
+	length = 0
+	for i := len(list) - 1; i >= 0; i-- {
+		if list[i] == blockId {
+			length++
+		} else {
+			if length != 0 {
+				return i + 1, length, true
+			}
+		}
+	}
+	return -1, -1, false
+}
+
+func compactBlocks2(list []int) (compacted []int) {
+	compacted = slices.Clone(list)
+	lastBlockIndex, _ := findLastUsedIndex(compacted)
+	lastBlockId := compacted[lastBlockIndex]
+	// fmt.Printf("i1 Checking block id %d\n", lastBlockId)
+	lastUsedStart, length, _ := findBlockById(compacted, lastBlockId)
+	firstEmpty, found := findFirstEmptyBlockOfLength(compacted, length)
+	for !found {
+		lastBlockId--
+		if lastBlockId < 0 {
+			return
+		}
+		// fmt.Printf("i2 Checking block id %d\n", lastBlockId)
+		lastUsedStart, length, _ = findBlockById(compacted, lastBlockId)
+		firstEmpty, found = findFirstEmptyBlockOfLength(compacted, length)
+	}
+	for {
+		// fmt.Printf(
+		// 	"Moving block %d starting at %d with len %d to %d\n",
+		// 	lastBlockId,
+		// 	lastUsedStart,
+		// 	length,
+		// 	firstEmpty,
+		// )
+		for i := range length {
+			util.SliceSwap(compacted, lastUsedStart+i, firstEmpty+i)
+		}
+		lastBlockId--
+		if lastBlockId < 0 {
+			return
+		}
+		// fmt.Printf("l1 Checking block id %d\n", lastBlockId)
+		lastUsedStart, length, _ = findBlockById(compacted, lastBlockId)
+		firstEmpty, found = findFirstEmptyBlockOfLength(compacted, length)
+		// startLastEmpty := findStartLastEmptyBlock(compacted)
+		// fmt.Printf("First empty found: %d, start last empty: %d\n", firstEmpty, startLastEmpty)
+		for !found || firstEmpty > lastUsedStart {
+			// fmt.Printf("No space for id %d found\n", lastBlockId)
+			lastBlockId--
+			if lastBlockId < 0 {
+				return
+			}
+			// fmt.Printf("l2 Checking block id %d\n", lastBlockId)
+			lastUsedStart, length, _ = findBlockById(compacted, lastBlockId)
+			firstEmpty, found = findFirstEmptyBlockOfLength(compacted, length)
+		}
+	}
+}
+
+func main() {
+	rawInput := []rune(string(util.LoadFileFromArgs()))
+	allNums := sliceutils.Map(
+		sliceutils.Filter(rawInput, func(t rune) bool { return unicode.IsNumber(t) }),
+		func(t rune) int { return other.Must(strconv.Atoi(string(t))) },
+	)
+	blocks := indicesToBlocks(allNums)
+	// fmt.Printf("Parsed blocks: %v\n", blocks)
+	compacted := compactBlocks1(blocks)
+	// fmt.Printf("Compacted blocks: %v\n", compacted)
+	onlySetBlocks := sliceutils.Filter(compacted, func(t int) bool { return t != EmptyBlockId })
+	checksum1 := checksumBlocks(onlySetBlocks)
+	fmt.Printf("Task 1: %d\n", checksum1)
+	compacted2 := compactBlocks2(blocks)
+	fmt.Printf(
+		"Task 2: %d\n",
+		checksumBlocks(
+			compacted2,
+		),
+	)
+}

day9/sample

@@ -0,0 +1 @@
+2333133121414131402