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package sort
import (
"algorithms/ds"
)
func Quick(a ds.ArrayList) ds.ArrayList {
Shuffle(a)
quick(a)
return a
}
func quick(a ds.ArrayList) {
if len(a) <= 10 {
Insertion(a)
return
}
j := quickPartition(a)
quick(a[0:j])
quick(a[j+1:])
}
func quickPartition(a ds.ArrayList) int {
i := 0 // Left scan index
j := len(a) // Right scan index
hi := j - 1
// Median of first 3 elems is partitioning item
// This works because we randomly shuffled a in the beginning
Insertion(a[0:3])
a.Swap(0, 1)
v := a[0] // Partitioning item
for {
for i++; a[i] < v && i < hi; i++ {
}
for j--; v < a[j] && j > 0; j-- {
}
// Check scan complete
if i >= j {
break
}
a.Swap(i, j)
}
// Put partitioning item v into a[j]
a.Swap(0, j)
// whith a[lo..j-1 <= a[j] <= a[j+1..hi]
return j
}
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