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parallel merge

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This commit is contained in:
Gregory 2021-12-16 21:33:57 +02:00
parent 08c76c5be5
commit 2ea8b8e388
1 changed files with 14 additions and 7 deletions
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21
sorting/merge.go
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@ -1,5 +1,7 @@
package sorting package sorting
import "sync"
func merge[T any](items []T, low, mid, hig int, less func(a, b T) bool, aux []T) { func merge[T any](items []T, low, mid, hig int, less func(a, b T) bool, aux []T) {
i, j := low, mid+1 i, j := low, mid+1
@ -26,8 +28,11 @@ func merge[T any](items []T, low, mid, hig int, less func(a, b T) bool, aux []T)
} }
func doSort[T any](items []T, low, hig int, less func(a, b T) bool, aux []T) { func doSort[T any](items []T, low, hig int, less func(a, b T) bool, aux []T) {
if hig <= low {
return
}
// Optimization 2: if array length is less then 15 // Optimization 2: if array length is less than 15
// it's imperically prooven that insertion sort // it's imperically prooven that insertion sort
// for such arrays can speed up merge sort up to 15% // for such arrays can speed up merge sort up to 15%
if hig-low <= 15 { if hig-low <= 15 {
@ -35,14 +40,16 @@ func doSort[T any](items []T, low, hig int, less func(a, b T) bool, aux []T) {
return return
} }
if hig <= low {
return
}
mid := low + (hig-low)/2 mid := low + (hig-low)/2
doSort(items, low, mid, less, aux) // Optimization 3: we can run sorting in parallel.
doSort(items, mid+1, hig, less, aux) // This is costly optimization because we increase memory
// usage by creating WaitGroup instances
wg := sync.WaitGroup{}
wg.Add(2)
go func() { doSort(items, low, mid, less, aux); wg.Done() }()
go func() { doSort(items, mid+1, hig, less, aux); wg.Done() }()
wg.Wait()
// Optimization 1: if two subarrays already sorted // Optimization 1: if two subarrays already sorted
// we can skip merging them // we can skip merging them