protype shuffling version -- unreachable

manualsort.go

@@ -6,15 +6,18 @@ import (
 	"bufio"
 	"fmt"
 	"log"
+	"math/rand"
 	"os"
 	"slices"
 	"strings"
+	"sync"
+	"time"
 )
 
 // handwritten merge sort because it minimizes comparisons, which are
 // the expensive part when asking a human for every comparison.
 // quicksort's "in-place" behavior isn't necessary.
-func merge(a, b []string) []string {
+func merge(a, b []string, less func(string, string) bool) []string {
 	if len(a) == 0 {
 		return b
 	}
@@ -23,7 +26,7 @@ func merge(a, b []string) []string {
 	}
 	ret := make([]string, 0, len(a)+len(b))
 	for len(a) > 0 && len(b) > 0 {
-		if better(a[0], b[0]) {
+		if less(a[0], b[0]) {
 			ret = append(ret, a[0])
 			a = a[1:]
 		} else {
@@ -50,6 +53,48 @@ var (
 	}
 )
 
+type Question struct {
+	First  string
+	Second string
+	Reply  chan<- bool
+}
+
+func (q *Question) Ask() {
+	q.Reply <- better(q.First, q.Second)
+}
+
+func (q *Question) Push(qc chan<- *Question) bool {
+	c := make(chan bool, 1)
+	q.Reply = c
+	qc <- q
+	return <-c
+}
+
+func betterLoop(qq <-chan *Question) {
+	var pool []*Question
+	drain := time.After(100 * time.Millisecond)
+	for {
+		select {
+		case q, ok := <-qq:
+			if !ok {
+				qq = nil
+				continue
+			}
+			pool = append(pool, q)
+		case <-drain:
+			rand.Shuffle(len(pool), func(i, j int) { pool[i], pool[j] = pool[j], pool[i] })
+			for _, q := range pool {
+				q.Ask()
+			}
+			pool = pool[:0]
+			if qq == nil {
+				return
+			}
+			drain = time.After(100 * time.Millisecond)
+		}
+	}
+}
+
 func better(first, second string) bool {
 	for {
 		fmt.Println()
@@ -74,12 +119,42 @@ func better(first, second string) bool {
 	}
 }
 
+func parallelBetter(first, second string, qq chan<- *Question) bool {
+	q := Question{
+		First:  first,
+		Second: second,
+	}
+	return q.Push(qq)
+}
+
 func mergeSort(items []string) []string {
 	if len(items) <= 1 {
 		return items
 	}
 	midpoint := len(items) / 2
-	return merge(mergeSort(items[:midpoint]), mergeSort(items[midpoint:]))
+	return merge(mergeSort(items[:midpoint]), mergeSort(items[midpoint:]), better)
+}
+
+func parallelMergeSort(questions chan<- *Question, items []string) []string {
+	if len(items) <= 1 {
+		return items
+	}
+	midpoint := len(items) / 2
+	var wg sync.WaitGroup
+	wg.Add(2)
+	var r1, r2 []string
+	go func() {
+		r1 = parallelMergeSort(questions, items[:midpoint])
+		wg.Done()
+	}()
+	go func() {
+		r2 = parallelMergeSort(questions, (items[midpoint:]))
+		wg.Done()
+	}()
+	wg.Wait()
+	return merge(r1, r2, func(a, b string) bool {
+		return parallelBetter(a, b, questions)
+	})
 }
 
 func main() {
@@ -107,6 +182,9 @@ func main() {
 		log.Fatalf("can't read %q: %v", os.Args[1], err)
 	}
 
+	rand.Shuffle(len(items), func(i, j int) {
+		items[i], items[j] = items[j], items[i]
+	})
 	sorted := mergeSort(items)
 	fmt.Println("Sorted. Saving...")
 	obuf := bufio.NewWriter(ofile)