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quicksort.go
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/
quicksort.go
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package clrs
import (
"math/rand"
)
func quicksort(a []int, p, r int) {
if p < r {
q := partition(a, p, r)
quicksort(a, p, q-1)
quicksort(a, q+1, r)
}
}
func partition(a []int, p, r int) int {
x := a[r]
i := p - 1
for j := p; j <= r-1; j++ {
if a[j] <= x {
i = i + 1
a[i], a[j] = a[j], a[i]
}
}
a[i+1], a[r] = a[r], a[i+1]
return i + 1
}
func randomizedPartition(a []int, p, r int) int {
i := rand.Intn(r-p+1) + p
a[r], a[i] = a[i], a[r]
return partition(a, p, r)
}
func randomizedQuicksort(a []int, p, r int) {
if p < r {
q := randomizedPartition(a, p, r)
randomizedQuicksort(a, p, q-1)
randomizedQuicksort(a, q+1, r)
}
}
func hoarePartition(a []int, p, r int) int {
x := a[p]
i := p - 1
j := r + 1
for {
for {
j = j - 1
if a[j] <= x {
break
}
}
for {
i = i + 1
if a[i] >= x {
break
}
}
if i < j {
a[i], a[j] = a[j], a[i]
} else {
return j
}
}
}
func hoareQuicksort(a []int, p, r int) {
if p <= r-1 {
q := hoarePartition(a, p, r)
hoareQuicksort(a, p, q)
hoareQuicksort(a, q+1, r)
}
}
func tailRecursiveQuicksort(a []int, p, r int) {
for p < r {
q := partition(a, p, r)
tailRecursiveQuicksort(a, p, q-1)
p = q + 1
}
}