question 9A

go/question9/main.go

@@ -0,0 +1,154 @@
+package main
+
+import (
+	"fmt"
+	"strconv"
+	"strings"
+)
+
+type Inode struct {
+	fileId int // inode with id -1 are empty
+	length int
+}
+
+func (inode *Inode) String() string {
+	v := ""
+	if inode.fileId < 0 {
+		v = "."
+	} else {
+		v = strconv.Itoa(inode.fileId)
+	}
+	return strings.Repeat(v, inode.length)
+}
+
+func (inode *Inode) IsFreeSpace() bool {
+	return inode.fileId < 0
+}
+
+func (inode *Inode) Copy() *Inode {
+	return &Inode{inode.fileId, inode.length}
+}
+
+type FileSystem struct {
+	inodes *DoubleLinkedList[*Inode]
+}
+
+func (fs *FileSystem) String() string {
+	ret := ""
+	for inode := range fs.inodes.Iter() {
+		ret += inode.String()
+	}
+	return ret
+
+}
+
+func (fs *FileSystem) CheckSum() int {
+	ret, idx := 0, 0
+	for inode := range fs.inodes.Iter() {
+		if inode.IsFreeSpace() {
+			idx += inode.length
+			continue
+		}
+		for j := 0; j < inode.length; j++ {
+			ret = ret + idx*inode.fileId
+			idx++
+		}
+	}
+	return ret
+}
+
+func parseString(s string) *FileSystem {
+	dll := NewDLL[*Inode]()
+	inode := &Inode{-1, 0}
+	for _, c := range s {
+		fileId := -1
+
+		if c != '.' {
+			fileId, _ = strconv.Atoi(string(c))
+		}
+		if inode.fileId == fileId {
+			inode.length += 1
+		} else {
+			dll.InsertLast(inode)
+			inode = &Inode{fileId, 1}
+		}
+	}
+	dll.InsertLast(inode)
+	if inode, ok := dll.Last(); !ok || !inode.IsFreeSpace() {
+		dll.InsertLast(&Inode{-1, 0})
+	}
+	return &FileSystem{dll}
+}
+
+func parseInput(input string) *FileSystem {
+	dll := NewDLL[*Inode]()
+	id := 0
+	for i, c := range input {
+		var inode *Inode
+		length, _ := strconv.Atoi(string(c))
+		if isFreeSpace := i%2 == 1; isFreeSpace {
+			inode = &Inode{-1, length}
+		} else {
+			inode = &Inode{id, length}
+			id++
+		}
+		dll.InsertLast(inode)
+	}
+	if inode, ok := dll.Last(); !ok || !inode.IsFreeSpace() {
+		dll.InsertLast(&Inode{-1, 0})
+	}
+	return &FileSystem{dll}
+}
+
+func (fs *FileSystem) takeFilesFromTheEnd(id DllId) *Inode {
+	for node, ok := fs.inodes.nodes[fs.inodes.LastNode]; ok; node, ok = fs.inodes.nodes[node.PreviousId] {
+		if node.Id == id {
+			break
+		}
+		if inode, _ := fs.inodes.GetById(node.Id); !inode.IsFreeSpace() && inode.length > 0 {
+			return inode
+		}
+	}
+	return nil
+}
+
+func (fs *FileSystem) OptimizeDiskFragmentation() {
+	emptySpaceAtTheEndId, _ := fs.inodes.LastId()
+	emptySpaceAtTheEnd, _ := fs.inodes.Last()
+	for discId, ok := fs.inodes.FirstId(); ok; discId, ok = fs.inodes.NextId(discId) {
+		freeSpaceInode, _ := fs.inodes.GetById(discId)
+		if !freeSpaceInode.IsFreeSpace() || discId == emptySpaceAtTheEndId {
+			continue
+		}
+		fileInodeAtTheEnd := fs.takeFilesFromTheEnd(discId)
+		if fileInodeAtTheEnd == nil {
+			break
+		}
+
+		if freeSpaceInode.length <= fileInodeAtTheEnd.length {
+			newInode := &Inode{fileInodeAtTheEnd.fileId, freeSpaceInode.length}
+			fs.inodes.InsertBefore(discId, newInode)
+			emptySpaceAtTheEnd.length += freeSpaceInode.length
+			fileInodeAtTheEnd.length -= freeSpaceInode.length
+			freeSpaceInode.length = 0
+		} else {
+			newFreeSpaceInode := &Inode{-1, freeSpaceInode.length - fileInodeAtTheEnd.length}
+			fs.inodes.InsertAfter(discId, newFreeSpaceInode)
+			fs.inodes.InsertBefore(discId, fileInodeAtTheEnd.Copy())
+			emptySpaceAtTheEnd.length += fileInodeAtTheEnd.length
+			fileInodeAtTheEnd.length = 0
+			freeSpaceInode.length = 0
+		}
+	}
+}
+
+func Question9A(input string) int {
+	fs := parseInput(input)
+	fs.OptimizeDiskFragmentation()
+	return fs.CheckSum()
+}
+
+func main() {
+	fmt.Println("The answer to question 9A is: ", Question9A(realInput))
+
+}