golang 实现跳表skiplist

Posted 2021-03-03 yanbiao

package main

import (
	"math/rand"
	"time"
	"fmt"
)

const (
	P = 0.6
	MaxLevel = 8
)

func randomLevel() int {
	i := 1
	rand.Seed(time.Now().UnixNano())
	for i < MaxLevel {
		p := rand.Float64()
		if (p < P) {
			i++
		} else {
			break
		}
	}
	return i
}

type node struct {
	level int
	nexts []*node
	v     int
}

type skipList struct {
	head *node
}

func NewSkipList() *skipList {
	s := new(skipList)
	s.head = new(node)
	s.head.level = MaxLevel
	s.head.nexts = make([]*node, MaxLevel)
	return s
}

func (s *skipList) insert(v int) {
	l := randomLevel()
	add := new(node)
	add.level = l
	add.nexts = make([]*node, l)
	add.v = v
	i := l

	p := s.head
	for i > 0 {
		n := p.nexts[i - 1]
		for n != nil && n.v < v {
			p = n
			n = n.nexts[i - 1]
		}
		p.nexts[i - 1] = add
		add.nexts[i - 1] = n
		i --
	}
}

func (s *skipList) search(v int) *node {
	i := s.head.level
	p := s.head
	for i > 0 {
		n := p.nexts[i - 1]
		for n != nil && n.v < v {
			p = n
			n = n.nexts[i - 1]
		}
		if n != nil && n.v == v {
			return n
		}
		i --
	}
	return nil
}

func (s *skipList) delete(d *node) {
	i := d.level
	p := s.head
	for i > 0 {
		n := p.nexts[i - 1]
		for n != nil && n.v < d.v {
			p = n
			n = n.nexts[i - 1]
		}
		p.nexts[i - 1] = d.nexts[i - 1]
		i --
	}
}

func (s *skipList) print() {
	p := s.head
	for (p.nexts[0] != nil) {
		fmt.Println(p.nexts[0].v)
		p = p.nexts[0]
	}
}

func main() {
	s := NewSkipList()
	s.insert(8)
	s.insert(5)
	s.insert(3)
	s.insert(7)
	s.insert(4)
	s.insert(9)
	s.insert(100)
	s.insert(101)
	s.insert(55)
	s.insert(20)
	s.insert(18)
	s.insert(11)
	s.insert(15)
	s.insert(33)
	s.print()

	for i := 0; i < 2; i++ {
		n := s.search(7)
		if n != nil {
			fmt.Println("found")
			s.delete(n)
		} else {
			fmt.Println("no found")
		}
	}

	s.print()
}