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skiplist.go
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/
skiplist.go
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package collection
import (
"golang.org/x/exp/constraints"
"golang.org/x/exp/rand"
)
/**
reference: https://ketansingh.me/posts/lets-talk-skiplist/
Hi,
Very interesting topic.
I just discovered go:notinheap pragma to tag a type as not garbage-collected. It could be interesting in such cases.
Max.
*/
type (
Record[K constraints.Ordered, V any] struct {
Key K
Value V
}
SkipNode[K constraints.Ordered, V any] struct {
record *Record[K, V]
forward []*SkipNode[K, V]
}
SkipList[K constraints.Ordered, V any] struct {
head *SkipNode[K, V]
level int
size int
}
)
func NewRecord[K constraints.Ordered, V any](key K,
value V) *Record[K, V] {
return &Record[K, V]{
Key: key,
Value: value,
}
}
func NewSkipNode[K constraints.Ordered, V any](key K,
value V, level int) *SkipNode[K, V] {
return &SkipNode[K, V]{
record: NewRecord(key, value),
forward: make([]*SkipNode[K, V], level+1),
}
}
func NewSkipList[K constraints.Ordered, V any]() *SkipList[K, V] {
return &SkipList[K, V]{
head: NewSkipNode[K, V](*new(K), *new(V), 0),
level: -1,
size: 0,
}
}
func (s *SkipList[K, V]) Insert(key K, value V) {
newLevel := s.getRandomLevel()
if newLevel > s.level {
s.adjustLevel(newLevel)
}
newNode := NewSkipNode[K, V](key, value, newLevel)
updates := make([]*SkipNode[K, V], newLevel+1)
x := s.head
for i := s.level; i >= 0; i-- {
for x.forward[i] != nil && x.forward[i].record.Key < key {
x = x.forward[i]
}
updates[i] = x
}
for i := 0; i <= newLevel; i++ {
newNode.forward[i] = updates[i].forward[i]
updates[i].forward[i] = newNode
}
s.size += 1
}
func (s *SkipList[K, V]) Find(key K) (V, bool) {
x := s.head
for i := s.level; i >= 0; i-- {
for {
if x.forward[i] == nil || x.forward[i].record.Key > key {
break
} else if x.forward[i].record.Key == key {
return x.forward[i].record.Value, true
} else {
x = x.forward[i]
}
}
}
return *new(V), false
}
func (s *SkipList[K, V]) Delete(key K) {
x := s.head
for i := s.level; i >= 0; i-- {
for {
if x.forward[i] == nil || x.forward[i].record.Key > key {
break
} else if x.forward[i].record.Key == key {
x.forward[i] = x.forward[i].forward[i]
} else {
x = x.forward[i]
}
}
}
}
func (s *SkipList[K, V]) adjustLevel(level int) {
temp := s.head.forward
s.head = NewSkipNode(*new(K), *new(V), level)
s.level = level
copy(s.head.forward, temp)
}
func (s *SkipList[K, V]) getRandomLevel() int {
level := 0
for rand.Int31()%2 == 0 {
level += 1
}
return level
}