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skiplist.go
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/
skiplist.go
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package util
import (
"math/rand"
)
const (
maxLevel = 16 // Should be enough for 2^16 elements
probability = 0.25 // It's the best practice value (Based on Time and Space)
// Higher level, smaller probability
// Just modify the probability factor P to reduce additional space
)
type slNode struct {
score float64
val interface{}
// forward[i]: the slNode is current node's next one, which is at i_th layer
forward []*slNode
}
type SlElement struct {
Score float64 `json:"score"`
Val interface{} `json:"val"`
}
func newSLNode(score float64, value interface{}, level int) *slNode {
return &slNode{
score: score,
val: value,
forward: make([]*slNode, level),
}
}
type SkipList struct {
header *slNode
len int
level int
}
func NewSkipList() *SkipList {
return &SkipList{
header: &slNode{forward: make([]*slNode, maxLevel)},
len: 0,
}
}
func randomLevel() int {
level := 1
for rand.Float32() < probability && level < maxLevel {
level++
}
return level
}
func (sl *SkipList) Front() *slNode {
return sl.header.forward[0]
}
func (n *slNode) Next() *slNode {
if n != nil {
return n.forward[0]
}
return nil
}
func (sl *SkipList) GetList() []SlElement {
list := make([]SlElement, sl.len)
x := sl.Front()
i := 0
for x != nil {
list[i] = SlElement{
Score: x.score,
Val: x.val,
}
x = x.Next()
i++
}
return list
}
func (sl *SkipList) Search(score float64) ([]*slNode, bool) {
x := sl.header
for i := sl.level - 1; i >= 0; i-- {
for x.forward[i] != nil && x.forward[i].score < score {
x = x.forward[i]
}
}
x = x.Next()
res := make([]*slNode, 0)
if x != nil && x.score == score {
for x != nil && x.score == score {
res = append(res, x)
x = x.Next()
}
return res, true
}
return nil, false
}
func (sl *SkipList) Insert(score float64, value interface{}) *slNode {
update := make([]*slNode, maxLevel)
x := sl.header
for i := sl.level - 1; i >= 0; i-- {
for x.forward[i] != nil && x.forward[i].score < score {
x = x.forward[i]
}
update[i] = x
}
x = x.Next()
level := randomLevel()
if level > sl.level {
level = sl.level + 1
update[sl.level] = sl.header
sl.level = level
}
newNode := newSLNode(score, value, level)
for i := 0; i < level; i++ {
newNode.forward[i] = update[i].forward[i]
update[i].forward[i] = newNode
}
sl.len++
return newNode
}
func (sl *SkipList) Delete(score float64) {
update := make([]*slNode, maxLevel)
x := sl.header
for i := sl.level - 1; i >= 0; i-- {
for x.forward[i] != nil && x.forward[i].score < score {
x = x.forward[i]
}
update[i] = x
}
x = x.Next()
for x != nil && x.score == score {
for i := 0; i < sl.level; i++ {
if update[i].forward[i] != x {
break
}
update[i].forward[i] = x.forward[i]
}
sl.len--
x = x.Next()
}
}
func (sl *SkipList) Len() int {
return sl.len
}