• 跳表(skipList)的原理和java实现


    写这个博客的原因是因为看其他人写的java实现的跳表代码总是有点看不懂,原理倒是比较清楚,所以自己动手写了一个简单的跳表,希望能给看这块儿数据结构的同学一个启发,原理我觉得这篇文章写的不错,推荐给大家:https://blog.csdn.net/pcwl1206/article/details/83512600?depth_1-utm_source=distribute.pc_relevant.none-task&utm_source=distribute.pc_relevant.none-task

    不多说,直接贴代码:

    package com.example.demo;
    
    import java.util.Random;
    
    /**
     * 跳表的实现
     */
    public class SkipList {
        public static final int MAX_LEVEL = 16; //跳表所允许的最大层级
        private SkipListNode head = new SkipListNode(null, MAX_LEVEL);
        private Random random = new Random();
        private int usedLevel = 1; //当前跳表使用中的最大层级
    
        public void insert(int value) {
            int level = randomLevel(); //找出当前插入值随机最大层数
            //遍历节点并插入
            insert(value, level);
    
        }
    
        public void delete(int value) {
            //从最高层开始,寻找节点
            int level = usedLevel;
            while(level >= 1) {
                level--;
                SkipListNode searchResult = search(value, level);
                if(searchResult != null) {
                    deleteNode(searchResult);
                    break;
                }
            }
    
        }
    
        //逐层打印
        public void print() {
           int level = usedLevel;
           while(level >= 1) {
               level--;
               printLevel(level);
           }
        }
    
        private void printLevel(int level) {
            SkipListNode current = head;
            String result = new String();
            while (current.next[level] != null) {
                result = result + current.next[level].data + " -> ";
                current = current.next[level];
            }
            System.out.println("第 " + level + " 层的数据为 : " + result);
        }
    
        private void deleteNode(SkipListNode searchResult) {
            //将当前节点的前置节点和后置节点关联起来即可
            int currentLevel = searchResult.getMaxlevel();
            while(currentLevel >= 1) {
                currentLevel--;
                //当前节点的前置节点的后置节点 = 当前节点的后置节点
                searchResult.pre[currentLevel].next[currentLevel] = searchResult.next[currentLevel];
                if(searchResult.next[currentLevel] != null) {
                    //如果当前节点的后置节点不为null
                    //当前节点的额后置节点的前置节点 = 当前节点的前置节点
                    searchResult.next[currentLevel].pre[currentLevel] = searchResult.pre[currentLevel];
                }
            }
        }
    
        private SkipListNode search(int value, int level) {
            //从头开始遍历
            SkipListNode current = head;
            while(current.next[level] != null && current.next[level].data < value) {
                current = current.next[level];
            }
            if(current.next[level] == null || current.next[level].data != value) {
                //如果搜索到最后,或者已经搜索到比寻找值大的节点了
                return null;
            }
            return current.next[level];
    
        }
    
        private void insert(int value, int level) {
            SkipListNode node = new SkipListNode(value, level); //构造当前节点
            int currentLevel = level;
            while(currentLevel-- > 0) {
                //从最高层开始,遍历每一层
                if(head.next[currentLevel] == null) {
                    //如果当前没有插入任何元素,直接插入即可
                    head.next[currentLevel] = node;
                    node.pre[currentLevel] = head;
                } else {
                    SkipListNode current = head.next[currentLevel], pre = head;
                    //从第一个元素开始遍历
                    while(current != null && current.data < value) {
                        pre = current;
                        current = current.next[currentLevel];
                    }
                    //设置前置节点的后置节点为当前节点
                    pre.next[currentLevel] = node;
                    node.pre[currentLevel] = pre;
                    if(current != null) {
                        //如果没有遍历到结尾,则需要设置当前节点的前置节点
                        current.pre[currentLevel] = node;
                        node.next[currentLevel] = current;
                    }
                }
    
            }
            usedLevel = usedLevel > level ? usedLevel : level;
        }
    
        //随机生成函数,即对于任意一个要插入跳表的节点,它的层级为多少
        private int randomLevel() {
            int level = 1;
            for(int i = 1; i < MAX_LEVEL; i++) {
                if(random.nextInt() % 2 == 1) {
                    level++;
                }
            }
            return level;
        }
    
    
        private class SkipListNode{
            private Integer data;
            private SkipListNode[] next; //后置节点
            private SkipListNode[] pre; //前置节点,方便删除使用
    
            public SkipListNode(Integer data, int maxLevel) {
                this.data = data;
                next = new SkipListNode[maxLevel];
                pre = new SkipListNode[maxLevel];
            }
    
            int getMaxlevel() {
                return next.length;
            }
    
        }
    
        public static void main(String[] args) {
            SkipList skipList = new SkipList();
            skipList.insert(10);
            skipList.insert(25);
            skipList.insert(83);
            skipList.insert(20);
            skipList.print();
            System.out.println("------------------");
            skipList.delete(83);
            skipList.delete(20);
            skipList.print();
    
        }
    }
    

      

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  • 原文地址:https://www.cnblogs.com/hermanlife/p/12497689.html
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