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|
package skip
import (
"fmt"
"math/rand"
"time"
)
type (
node struct {
next []*node
key interface{}
value interface{}
}
SkipList struct {
root *node
size int
less func(interface{},interface{})bool
gen *rand.Rand
probability float64
}
)
// Create a new skip list
func New(less func(interface{},interface{})bool) *SkipList {
gen := rand.New(rand.NewSource(time.Now().UnixNano()))
n := &node{make([]*node, 0),nil,nil}
return &SkipList{n, 0, less, gen, 0.75}
}
func (this *SkipList) Do(f func(interface{}, interface{})bool) {
if this.size == 0 {
return
}
cur := this.root.next[0]
for cur != nil {
if !f(cur.key, cur.value) {
break
}
cur = cur.next[0]
}
}
// Get an item from the skip list
func (this *SkipList) Get(key interface{}) interface{} {
if this.size == 0 {
return nil
}
cur := this.root
// Start at the top
for i := len(cur.next)-1; i >= 0; i-- {
for this.less(cur.next[i].key, key) {
cur = cur.next[i]
}
}
cur = cur.next[0]
if this.equals(cur.key, key) {
return cur.value
}
return nil
}
// Insert a new item into the skip list
func (this *SkipList) Insert(key interface{}, value interface{}) {
prev := this.getPrevious(key)
// Already in the list so just update the value
if len(prev) > 0 && prev[0].next[0] != nil && this.equals(prev[0].next[0].key, key) {
prev[0].next[0].value = value
return
}
h := len(this.root.next)
nh := this.pickHeight()
n := &node{make([]*node, nh),key,value}
// Higher than anything seen before, so tack it on top
if nh > h {
this.root.next = append(this.root.next, n)
}
// Update the previous nodes
for i := 0; i < h && i < nh; i++ {
n.next[i] = prev[i].next[i]
prev[i].next[i] = n
}
this.size++
}
// Get the length of the skip list
func (this *SkipList) Len() int {
return this.size
}
// Remove an item from the skip list
func (this *SkipList) Remove(key interface{}) interface{} {
prev := this.getPrevious(key)
if len(prev) == 0 {
return nil
}
cur := prev[0].next[0]
// If we found it
if cur != nil && this.equals(key, cur.key) {
// Change all the linked lists
for i := 0; i < len(prev); i++ {
if prev[i] != nil && prev[i].next[i] != nil {
prev[i].next[i] = cur.next[i]
}
}
// Kill off the upper links if they're nil
for i := len(this.root.next)-1; i>=0; i-- {
if this.root.next[i] == nil {
this.root.next = this.root.next[:i]
} else {
break
}
}
this.size--
return cur.value
}
return nil
}
// String representation of the list
func (this *SkipList) String() string {
str := "{"
if len(this.root.next) > 0 {
cur := this.root.next[0]
for cur != nil {
str += fmt.Sprint(cur.key)
str += ":"
str += fmt.Sprint(cur.value)
str += " "
cur = cur.next[0]
}
}
str += "}"
return str
}
// Get a vertical list of nodes of all the things that occur
// immediately before "key"
func (this *SkipList) getPrevious(key interface{}) []*node {
cur := this.root
h := len(cur.next)
nodes := make([]*node, h)
for i := h-1; i >= 0; i-- {
for cur.next[i] != nil && this.less(cur.next[i].key, key) {
cur = cur.next[i]
}
nodes[i] = cur
}
return nodes
}
// Defines an equals method in terms of "less"
func (this *SkipList) equals(a, b interface{}) bool {
return !this.less(a,b) && !this.less(b,a)
}
// Pick a random height
func (this *SkipList) pickHeight() int {
h := 1
for this.gen.Float64() > this.probability {
h++
}
if h > len(this.root.next) {
return h + 1
}
return h
}
|
