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package main
import (
"bufio"
"container/heap"
"fmt"
"os"
"sort"
"strconv"
"strings"
)
type FileReader struct {
file *os.File
scanner *bufio.Scanner
currentValue int
hasData bool
fileID int
}
func NewFileReader(filename string, id int) (*FileReader, error) {
file, err := os.Open(filename)
if err != nil {
return nil, err
}
fr := &FileReader{
file: file,
scanner: bufio.NewScanner(file),
fileID: id,
}
fr.hasData = fr.readNext()
return fr, nil
}
func (fr *FileReader) readNext() bool {
if fr.scanner.Scan() {
if val, err := strconv.Atoi(strings.TrimSpace(fr.scanner.Text())); err == nil {
fr.currentValue = val
return true
}
}
fr.hasData = false
fr.file.Close()
return false
}
type FileReaderHeap []*FileReader
func (h FileReaderHeap) Len() int { return len(h) }
func (h FileReaderHeap) Less(i, j int) bool { return h[i].currentValue < h[j].currentValue }
func (h FileReaderHeap) Swap(i, j int) { h[i], h[j] = h[j], h[i] }
func (h *FileReaderHeap) Push(x interface{}) {
*h = append(*h, x.(*FileReader))
}
func (h *FileReaderHeap) Pop() interface{} {
old := *h
n := len(old)
item := old[n-1]
*h = old[0 : n-1]
return item
}
type ExternalSorter struct {
chunkSize int
tempDir string
}
func NewExternalSorter(memoryLimitMB int) *ExternalSorter {
return &ExternalSorter{
chunkSize: (memoryLimitMB * 1024 * 1024) / 4, // 4 bytes per int
tempDir: "/tmp/",
}
}
func (es *ExternalSorter) sortAndSaveChunks(inputFile string) ([]string, error) {
file, err := os.Open(inputFile)
if err != nil {
return nil, err
}
defer file.Close()
var tempFiles []string
var buffer []int
chunkID := 0
scanner := bufio.NewScanner(file)
for scanner.Scan() {
if val, err := strconv.Atoi(strings.TrimSpace(scanner.Text())); err == nil {
buffer = append(buffer, val)
if len(buffer) == es.chunkSize {
tempFile := fmt.Sprintf("%schunk_%d.txt", es.tempDir, chunkID)
chunkID++
sort.Ints(buffer)
if err := es.writeChunk(buffer, tempFile); err != nil {
return nil, err
}
tempFiles = append(tempFiles, tempFile)
buffer = buffer[:0] // Clear buffer
}
}
}
// Handle remaining elements
if len(buffer) > 0 {
tempFile := fmt.Sprintf("%schunk_%d.txt", es.tempDir, chunkID)
sort.Ints(buffer)
if err := es.writeChunk(buffer, tempFile); err != nil {
return nil, err
}
tempFiles = append(tempFiles, tempFile)
}
return tempFiles, nil
}
func (es *ExternalSorter) writeChunk(data []int, filename string) error {
file, err := os.Create(filename)
if err != nil {
return err
}
defer file.Close()
writer := bufio.NewWriter(file)
for _, val := range data {
fmt.Fprintln(writer, val)
}
return writer.Flush()
}
func (es *ExternalSorter) mergeChunks(tempFiles []string, outputFile string) error {
output, err := os.Create(outputFile)
if err != nil {
return err
}
defer output.Close()
writer := bufio.NewWriter(output)
defer writer.Flush()
h := &FileReaderHeap{}
heap.Init(h)
// Initialize file readers
for i, tempFile := range tempFiles {
if reader, err := NewFileReader(tempFile, i); err == nil && reader.hasData {
heap.Push(h, reader)
}
}
for h.Len() > 0 {
current := heap.Pop(h).(*FileReader)
fmt.Fprintln(writer, current.currentValue)
if current.readNext() {
heap.Push(h, current)
}
}
// Clean up temporary files
for _, tempFile := range tempFiles {
os.Remove(tempFile)
}
return nil
}
func (es *ExternalSorter) ExternalSort(inputFile, outputFile string) error {
tempFiles, err := es.sortAndSaveChunks(inputFile)
if err != nil {
return err
}
return es.mergeChunks(tempFiles, outputFile)
}
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