Java实现跳表

本文主要是介绍Java实现跳表，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

简介

链表是一种基本的数据结构，而跳表是一种特殊的链表。跳表的每一个节点都有四个指针，上、下、左、右。当进行数据查询时，可以从最顶层开始查找，并可以向下移动，从而提高查询效率。

基本结构

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查找数的基本步骤

从最左上角的head开始，假如当前数等于目标数，直接返回；假如当前数右指针的数小于目标数，向右移动；假如当前数右指针的数大于目标数，向下移动。
当down指针为null时，没有找到。

Java节点结构

private class Node<T> {//score不能为负数long score;T value;Node up, down, left, right;public Node(T value) {this.score = -1;this.value = value;}public Node(long score, T value) {this.score = score;this.value = value;}@Overridepublic String toString() {return "Node{" +"score=" + score +", value=" + value +", up=" + up +", down=" + down +", left=" + left +", right=" + right +'}';}
}

Java实现跳表代码

private class SkipList<T> {// 最上层链表的头指针private Node<T> head;// 最上层聊表的尾指针private Node<T> tail;// 跳表的层数private int level;// 插入链表元素的个数private int size;// 用来生成随机数private Random random;public SkipList() {this.head = new Node(Long.MIN_VALUE, null);this.tail = new Node(Long.MAX_VALUE, null);this.level = 1;this.size = 0;this.random = new Random();this.head.right = this.tail;this.tail.left = this.head;}//判断跳表中是否有指定score的节点public boolean contain(long score) {Node help = head;while (help != null) {if (help.score == score) {return true;} else if (help.right.score > score) {help = help.down;} else if (help.right.score <= score) {help = head.right;}}return false;}//返回指定score的元素public Node find(long score) {Node help = head;while (help != null) {if (help.score == score) {return help;} else if (help.right.score > score) {help = help.down;} else if (help.right.score <= score) {help = head.right;}}return null;}//在最底层，找到指定score节点的前面一个节点,public Node findPreNode(long score) {//拿到最底层的head指针,从头开始判断最底部的链表，效率不行//Node help = headToButtom();Node help = head;//开始查询指定score节点的前面一个节点。如果链表中有指定score的节点，则返回相同节点的前面一个节点while (true) {if (score <= help.right.score) {if (help.down == null) return help;else help = help.down;} else {help = help.right;}}}//返回最底层的head指针private Node headToButtom() {Node help = head;while (help.down != null) {help = help.down;}return help;}//判断跳表是否为空public boolean isEmpty() {return size != 0;}//打印最底层的所有节点public void printAll() {Node help = headToButtom();while (help != null) {System.out.println(help);help = help.right;}}//插入节点public void insert(long score, T value) {//找到目标位置的前一个节点Node pre = findPreNode(score);//判断后面节点是否是和要插入节点一样的scoreif (pre.right.score == score) {pre = pre.right;while (pre != null) {pre.value = value;pre = pre.up;}return;}//插入节点Node target = new Node(score, value);target.left = pre;target.right = pre.right;pre.right.left = target;pre.right = target;//当前所属的层级int currLevel = 1;//随机往上沿升while (random.nextDouble() > 0.5) {currLevel++;if (currLevel <= level) {//不用再最上层生成一个新的链表Node upNode = new Node(score, value);Node right = target.right;while (right.up == null) {right = right.right;}right = right.up;Node left = target.left;while (left.up == null) {left = left.left;}left = left.up;upNode.left = left;left.right = upNode;upNode.right = right;right.left = upNode;target = upNode;} else {//需要在最上方生成一个新的链表this.level++;Node upNode = new Node(score, value);Node upHead = new Node(Long.MIN_VALUE, null);Node upTail = new Node(Long.MAX_VALUE, null);upHead.right = upNode;upNode.left = upHead;upTail.left = upNode;upNode.right = upTail;target = upNode;upHead.down = this.head;this.head.up = upHead;this.head = upHead;upTail.down = this.tail;this.tail.up = upTail;this.tail = upTail;}}}//通过分值移除某一个节点public boolean remove(long score) {//先找到最底层的节点Node target = find(score);if (target == null) {return false;} else {while (target != null) {target.left.right = target.right;target.right.left = target.left;target = target.up;}return true;}}//移除某一个节点public void remove(Node node) {while (node != null) {node.left.right = node.right;node.right.left = node.left;node = node.up;}}//范围删除,包括startScore的节点public void rangeRemove(long startScore) {//找到目标位置的前一个节点Node pre = findPreNode(startScore);while (pre.right.score < Long.MAX_VALUE) {remove(pre.right);}}//范围删除,包括startScore的节点,包括endScore的节点public void rangeRemove(long startScore, long endScore) {//找到目标位置的前一个节点Node pre = findPreNode(startScore);while (pre.right.score <= endScore) {remove(pre.right);}}//包括startScore之后的节点数目public int getNodeCount(long startScore) {int result = 0;//找到目标位置的前一个节点Node pre = findPreNode(startScore);while (pre.right.score < Long.MAX_VALUE) {result++;pre = pre.right;}return result;}//获取包括startScore的节点,包括endScore的节点的节点数目public int getNodeCount(long startScore, long endScore) {int result = 0;//找到目标位置的前一个节点Node pre = findPreNode(startScore);while (pre.right.score <= endScore) {result++;pre = pre.right;}return result;}private class Node<T> {//score不能为负数long score;T value;Node up, down, left, right;public Node(T value) {this.score = -1;this.value = value;}public Node(long score, T value) {this.score = score;this.value = value;}@Overridepublic String toString() {return "Node{" +"score=" + score +", value=" + value +", up=" + up +", down=" + down +", left=" + left +", right=" + right +'}';}}}