From ff4a4b2023cc3bf8af1e8b7581cadba2d7210305 Mon Sep 17 00:00:00 2001
From: Sebastian Steger <s.steger@hs-mannheim.de>
Date: Wed, 20 Aug 2025 11:36:36 +0000
Subject: [PATCH] merge sort

---
 go/05-concurrency/mergeSort.go | 105 ++++++++++++++++++++++++++++++++-
 1 file changed, 103 insertions(+), 2 deletions(-)

diff --git a/go/05-concurrency/mergeSort.go b/go/05-concurrency/mergeSort.go
index 4160246..53e2ebd 100644
--- a/go/05-concurrency/mergeSort.go
+++ b/go/05-concurrency/mergeSort.go
@@ -4,9 +4,108 @@ import (
 	"fmt"
 	"math/rand"
 	"sort"
+	"sync"
 	"time"
 )
 
+func mergeSortChannelsInternal(data []float64, sorted chan<- float64) {
+	defer close(sorted)
+
+	if len(data) <= 10000 {
+		sortedData := make([]float64, len(data))
+		copy(sortedData, data)
+		mergeSortSequential(sortedData)
+		for _, x := range sortedData {
+			sorted <- x
+		}
+	} else {
+		mid := len(data) / 2
+		left := data[:mid]
+		right := data[mid:]
+
+		sortedLeft := make(chan float64, 1000)
+		sortedRight := make(chan float64, 1000)
+
+		go mergeSortChannelsInternal(left, sortedLeft)
+		go mergeSortChannelsInternal(right, sortedRight)
+		mergeChannels(sortedLeft, sortedRight, sorted)
+	}
+}
+
+func mergeChannels(a, b <-chan float64, out chan<- float64) {
+	var okA, okB bool
+	var valA, valB float64
+
+	for {
+		if !okA {
+			valA, okA = <-a
+		}
+
+		if !okB {
+			valB, okB = <-b
+		}
+
+		if !okA && !okB {
+			break
+		}
+
+		if !okA {
+			out <- valB
+			okB = false
+			continue
+		}
+
+		if !okB {
+			out <- valA
+			okA = false
+			continue
+		}
+
+		if valA < valB {
+			out <- valA
+			okA = false
+		} else {
+			out <- valB
+			okB = false
+		}
+	}
+}
+
+func mergeSortChannels(data []float64) {
+	sorted := make(chan float64, 1000)
+	go mergeSortChannelsInternal(data, sorted)
+
+	sortedData := make([]float64, len(data))
+	i := 0
+	for x := range sorted {
+		sortedData[i] = x
+		i++
+	}
+
+	copy(data, sortedData)
+}
+
+func mergeSortParallel(data []float64) {
+	if len(data) <= 10000 {
+		mergeSortSequential(data)
+		return
+	}
+
+	mid := len(data) / 2
+	left := data[:mid]
+	right := data[mid:]
+
+	var wg sync.WaitGroup
+	wg.Add(2)
+
+	go func() { mergeSortParallel(left); wg.Done() }()
+	go func() { mergeSortParallel(right); wg.Done() }()
+
+	wg.Wait()
+
+	copy(data, merge(left, right))
+}
+
 func mergeSortSequential(data []float64) {
 	if len(data) <= 1 {
 		return
@@ -45,7 +144,7 @@ func merge(left, right []float64) []float64 {
 func main() {
 
 	//1. DATA CREATION
-	data := make([]float64, 1000*1000*20)
+	data := make([]float64, 1000*1000*20) //*1000*20)
 
 	for i := range data {
 		data[i] = rand.Float64() * 100 // Random floats between 0 and 100
@@ -58,7 +157,9 @@ func main() {
 	//2. SORTING
 	start := time.Now()
 
-	mergeSortSequential(data)
+	//mergeSortSequential(data)
+	//mergeSortParallel(data)
+	mergeSortChannels(data)
 
 	elapsed := time.Since(start)
 	fmt.Printf("MergeSort took %s\n", elapsed)