day9: first part solved

Author: fxnn

day9/example.txt

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

day9/main.go

@@ -0,0 +1,90 @@
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+
+	"github.com/fxnn/adventofcode2024/util"
+)
+
+const FREE = -1
+
+func calculateDiskBlocks(diskMap string) []int {
+	var diskBlocks = []int{}
+
+	var freeSpace = false
+	var fileId = 0
+	for _, b := range diskMap {
+		var blockCount = util.Atoi(string(b))
+		var blockUsage int
+		if freeSpace {
+			blockUsage = FREE
+		} else {
+			blockUsage = fileId
+			fileId++
+		}
+		diskBlocks = append(diskBlocks, util.Times(blockCount, blockUsage)...)
+		freeSpace = !freeSpace
+	}
+
+	return diskBlocks
+}
+
+func printDiskBlocks(diskBlocks []int) {
+	for _, b := range diskBlocks {
+		if b == FREE {
+			fmt.Print(".")
+		} else {
+			fmt.Printf("%d", b)
+		}
+	}
+}
+
+func compact(in []int) []int {
+	var out = make([]int, len(in))
+	var j = len(out) - 1
+	for i := range in {
+		for j >= 0 && in[j] == FREE {
+			j--
+		}
+		if i > j {
+			out[i] = FREE
+		} else if in[i] == FREE {
+			out[i] = in[j]
+			j--
+		} else {
+			out[i] = in[i]
+		}
+	}
+	return out
+}
+
+func checksum(diskBlocks []int) int {
+	var checksum = 0
+	for i, b := range diskBlocks {
+		if b != FREE {
+			checksum += i * b
+		}
+	}
+	return checksum
+}
+
+func main() {
+	scanner := bufio.NewScanner(os.Stdin)
+	scanner.Split(bufio.ScanLines)
+
+	scanner.Scan()
+	var diskMap = scanner.Text()
+
+	var diskBlocks = calculateDiskBlocks(diskMap)
+	printDiskBlocks(diskBlocks)
+	fmt.Println()
+
+	diskBlocks = compact(diskBlocks)
+	printDiskBlocks(diskBlocks)
+	fmt.Println()
+
+	var checksum = checksum(diskBlocks)
+	fmt.Printf("checksum: %d\n", checksum)
+}

util/slice.go

@@ -0,0 +1,27 @@
+package util
+
+import "fmt"
+
+func Times[T any](size int, value T) []T {
+	a := make([]T, size)
+  for i := range a {
+		a[i] = value
+	}
+	return a
+}
+
+// RemoveElement removes element with given index from slice
+func RemoveElement(slice []int, index int) ([]int, error) {
+	if index < 0 || index >= len(slice) {
+		return nil, fmt.Errorf("index out of range")
+	}
+
+	// Create a new slice and copy the elements before the index
+	newSlice := make([]int, 0, len(slice)-1)
+	newSlice = append(newSlice, slice[:index]...)
+
+	// Append the elements after the index
+	newSlice = append(newSlice, slice[index+1:]...)
+
+	return newSlice, nil
+}

util/util.go

@@ -52,19 +52,3 @@ func Sign(x int) int {
 	}
 	return -1
 }
-
-// RemoveElement removes element with given index from slice
-func RemoveElement(slice []int, index int) ([]int, error) {
-	if index < 0 || index >= len(slice) {
-		return nil, fmt.Errorf("index out of range")
-	}
-
-	// Create a new slice and copy the elements before the index
-	newSlice := make([]int, 0, len(slice)-1)
-	newSlice = append(newSlice, slice[:index]...)
-
-	// Append the elements after the index
-	newSlice = append(newSlice, slice[index+1:]...)
-
-	return newSlice, nil
-}