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skiplist.go
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skiplist.go
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// Copyright 2014, Shuhei Tanuma. All rights reserved.
// Use of this source code is governed by a MIT license
// that can be found in the LICENSE file.
//
// This skiplist implementation is almost re implementation of the redis's
// Skiplist implementation. As to understanding Skiplist algorithm and easy to re use.
//
// see also redis/src/t_zset.c
// Copyright (c) 2009-2012, Salvatore Sanfilippo <antirez at gmail dot com>
// Copyright (c) 2009-2012, Pieter Noordhuis <pcnoordhuis at gmail dot com>
// All rights reserved.
//
package skiplist
import (
"fmt"
"math/rand"
)
const (
MAX_LEVEL = 32
)
type Comparator interface {
// NOTE: skiplist will be ascending order if a < b, otherwise descending
Compare(interface{}, interface{}) int
}
type SkipListLevel struct {
Forward *SkipListNode
Span int
}
type SkipListNode struct {
Score interface{}
Data interface{}
Level map[int]*SkipListLevel
}
type SkipList struct {
Header *SkipListNode
Tail *SkipListNode
Length int
MaxLevel int
Level int
Comparator Comparator
}
func CreateSkiplistNode(level int, score interface{}, data interface{}) (*SkipListNode, error) {
node := &SkipListNode{
Level: map[int]*SkipListLevel{},
}
for i := 0; i < level; i++ {
node.Level[i] = &SkipListLevel{
Forward: nil,
Span: 0,
}
}
node.Score = score
node.Data = data
return node, nil
}
func NewSkipList(c Comparator) *SkipList {
list := &SkipList{
MaxLevel: MAX_LEVEL,
Level: 1,
}
list.Header, _ = CreateSkiplistNode(MAX_LEVEL, 0, 0)
list.Comparator = c
return list
}
func (self *SkipList) Insert(score, data interface{}) {
update := make(map[int]*SkipListNode)
rank := make(map[int]int)
node := self.Header
for i := self.Level - 1; i >= 0; i-- {
for node.Level[i].Forward != nil &&
self.Comparator.Compare(node.Level[i].Forward.Score, score) == -1 {
rank[i] += node.Level[i].Span
node = node.Level[i].Forward
}
update[i] = node
}
level := self.getRandomLevel()
if level > self.Level {
for i := self.Level; i < level; i++ {
rank[i] = 0
update[i] = self.Header
update[i].Level[i].Span = self.Length
}
self.Level = level
}
add, err := CreateSkiplistNode(level, score, data)
if err != nil {
panic(fmt.Sprintf("Error: %s", err))
}
for i := 0; i < level; i++ {
add.Level[i].Forward = update[i].Level[i].Forward
update[i].Level[i].Forward = add
add.Level[i].Span = update[i].Level[i].Span - (rank[i] - rank[i])
update[i].Level[i].Span = (rank[i] - rank[i]) + 1
}
for i := level; i < self.Level; i++ {
update[i].Level[i].Span++
}
self.Length++
}
func (self *SkipList) Delete(score interface{}) {
update := make(map[int]*SkipListNode)
node := self.Header
for i := self.Level - 1; i >= 0; i-- {
for node.Level[i].Forward != nil &&
self.Comparator.Compare(node.Level[i].Forward.Score, score) == -1 {
node = node.Level[i].Forward
}
update[i] = node
}
node = node.Level[0].Forward
if node != nil && self.Comparator.Compare(score, node.Score) == 0 {
self.deleteNode(node, score, update)
freeSkipListNode(node)
}
}
func (self *SkipList) deleteNode(node *SkipListNode, score interface{}, update map[int]*SkipListNode) {
for i := 0; i < self.Level; i++ {
if update[i].Level[i].Forward == node {
update[i].Level[i].Span += node.Level[i].Span - 1
update[i].Level[i].Forward = node.Level[i].Forward
} else {
update[i].Level[i].Span -= 1
}
}
for self.Level > 1 && self.Header.Level[self.Level-1].Forward == nil {
self.Level--
}
self.Length--
}
func (self *SkipList) getRandomLevel() int {
level := 1
for {
v := (rand.Int() & 0xFFFF)
if float64(v) < (0.25 * 0xFFFF) {
level++
} else {
break
}
}
if level < MAX_LEVEL {
return level
} else {
return MAX_LEVEL
}
}
func freeSkipListNode(node *SkipListNode) {
node.Score = nil
node.Data = nil
node.Level = nil
}