61 lines
1.1 KiB
Go
61 lines
1.1 KiB
Go
package sorting
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func merge[T any](items []T, low, mid, hig int, less func(a, b T) bool, aux []T) {
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i, j := low, mid+1
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for k := low; k <= hig; k++ {
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aux[k] = items[k]
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}
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for k := low; k <= hig; k++ {
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if i > mid {
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items[k] = aux[j]
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j++
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} else if j > hig {
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items[k] = aux[i]
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i++
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} else if less(aux[i], aux[j]) {
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items[k] = aux[i]
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i++
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} else {
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items[k] = aux[j]
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j++
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}
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}
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}
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func doSort[T any](items []T, low, hig int, less func(a, b T) bool, aux []T) {
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// Optimization 2: if array length is less then 15
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// it's imperically prooven that insertion sort
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// for such arrays can speed up merge sort up to 15%
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if hig-low <= 15 {
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Insertion(items[low:hig+1], less)
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return
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}
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if hig <= low {
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return
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}
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mid := low + (hig-low)/2
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doSort(items, low, mid, less, aux)
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doSort(items, mid+1, hig, less, aux)
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// Optimization 1: if two subarrays already sorted
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// we can skip merging them
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if less(items[mid], items[mid+1]) {
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return
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}
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merge(items, low, mid, hig, less, aux)
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}
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func Merge[T any](items []T, less func(a, b T) bool) {
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len := len(items)
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doSort(items, 0, len-1, less, make([]T, len))
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}
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