跳跃表
思想不再赘述，直接贴代码：
SkipListNode.java
package com.kuber.algorithmtest.skiplist;
public class SkipListNode <T>{
private int key;
private T value;
public SkipListNode<T> up, down, left, right; // 上下左右 四个指针
public static final int HEAD_KEY = Integer.MIN_VALUE; // 负无穷
public static final int TAIL_KEY = Integer.MAX_VALUE; // 正无穷
public SkipListNode(int k, T v) {
key = k;
value = v;
}
public int getKey() {
return key;
}
public void setKey(int key) {
this.key = key;
}
public T getValue() {
return value;
}
public void setValue(T value) {
this.value = value;
}
public boolean equals(Object o) {
if (this == o) {
return true;
}
if (o == null) {
return false;
}
if (!(o instanceof SkipListNode<?>)) {
return false;
}
SkipListNode<T> ent;
try {
ent = (SkipListNode<T>) o; // 检测类型
} catch (ClassCastException ex) {
return false;
}
return (ent.getKey() == key) && (ent.getValue() == value);
}
@Override
public String toString() {
return "key=value:" + key + "=" + value;
}
}
SkipList.java：
package com.kuber.algorithmtest.skiplist;
import java.util.Random;
public class SkipList <T>{
private SkipListNode<T> head,tail;
private int nodes; // 节点总数
private int listLevel; // 最大层数
private Random random; // 随机数，用于投掷硬币决定是否要加层高
private static final double PROBABILITY = 0.25; // 向上提升一个的概率（此处采用redis中的默认值）
private static final int MAXLEVEL = 32; // 最大层高（此处采用redis中的默认值）
public SkipList() {
random = new Random();
clear();
}
/**
* @Description: 清空跳跃表
* @Param: []
* @return: void
* @Author: kuber
*/
public void clear(){
head = new SkipListNode<T>(SkipListNode.HEAD_KEY, null);
tail = new SkipListNode<T>(SkipListNode.TAIL_KEY, null);
horizontalLink(head, tail);
listLevel = 0;
nodes = 0;
}
public boolean isEmpty(){
return nodes == 0;
}
public int size() {
return nodes;
}
/**
* @Description: 找到要插入的位置前面的那个key 的最底层节点
* @Param: [key]
* @return: com.jet.SkipListNode<T>
* @Author: kuber
*/
private SkipListNode<T> findNode(int key){
SkipListNode<T> p = head;
while(true){
while (p.right.getKey() != SkipListNode.TAIL_KEY && p.right.getKey() <= key) {
p = p.right;
}
if (p.down != null) {
p = p.down;
} else {
break;
}
}
return p;
}
/**
* @Description: 查找是否存在key，存在则返回该节点，否则返回null
* @Param: [key]
* @return: com.wailian.SkipListNode<T>
* @Author: kuber
*/
public SkipListNode<T> search(int key){
SkipListNode<T> p = findNode(key);
if (key == p.getKey()) {
return p;
} else {
return null;
}
}
/**
* @Description: 向跳跃表中添加key-value
* @Param: [k, v]
* @return: void
* @Author: kuber
*/
public void put(int k,T v){
SkipListNode<T> p = findNode(k);
// 如果key值相同，替换原来的value即可结束
if (k == p.getKey()) {
p.setValue(v);
return;
}
SkipListNode<T> q = new SkipListNode<>(k, v);
backLink(p, q);
int currentLevel = 0; // 当前所在的层级是0
// 抛硬币
while (random.nextDouble() < PROBABILITY && currentLevel < MAXLEVEL) {
// 如果超出了高度，需要重新建一个顶层
if (currentLevel >= listLevel) {
listLevel++;
SkipListNode<T> p1 = new SkipListNode<>(SkipListNode.HEAD_KEY, null);
SkipListNode<T> p2 = new SkipListNode<>(SkipListNode.TAIL_KEY, null);
horizontalLink(p1, p2);
verticalLink(p1, head);
verticalLink(p2, tail);
head = p1;
tail = p2;
}
// 将p移动到上一层
while (p.up == null) {
p = p.left;
}
p = p.up;
SkipListNode<T> e = new SkipListNode<>(k, null); // 只保存key就ok
backLink(p, e); // 将e插入到p的后面
verticalLink(e, q); // 将e和q上下连接
q = e;
currentLevel++;
}
nodes++; // 层数递增
}
/**
* @Description: node1后面插入node2
* @Param: [node1, node2]
* @return: void
* @Author: kuber
*/
private void backLink(SkipListNode<T> node1,SkipListNode<T> node2){
node2.left = node1;
node2.right = node1.right;
node1.right.left = node2;
node1.right = node2;
}
/**
* @Description: 水平双向连接
* @Param: [node1, node2]
* @return: void
* @Author: kuber
*/
private void horizontalLink(SkipListNode<T> node1,SkipListNode<T> node2){
node1.right = node2;
node2.left = node1;
}
/**
* @Description: 垂直双向连接
* @Param: [node1, node2]
* @return: void
* @Author: kuber
*/
private void verticalLink(SkipListNode<T> node1, SkipListNode<T> node2){
node1.down = node2;
node2.up = node1;
}
@Override
public String toString() {
if (isEmpty()) {
return "跳跃表为空！！！";
}
StringBuilder builder = new StringBuilder();
SkipListNode<T> p=head;
while (p.down != null) {
p = p.down;
}
while (p.left != null) {
p = p.left;
}
if (p.right!= null) {
p = p.right;
}
while (p.right != null) {
builder.append(p).append("\n");
p = p.right;
}
return builder.toString();
}
}
junit单元测试：
package com.kuber.algorithmtest.skiplist;
import org.junit.Test;
public class SkipListTest {
@Test
public void test1(){
SkipList<String> list = new SkipList<>();
System.out.println(list);
System.out.println("添加数据：");
list.put(6, "！！！");
list.put(1, "Ni Wenhan");
list.put(2, "make");
list.put(3, "SkipList");
list.put(1, "kuber");
list.put(4, "come true");
list.put(5, "successfully");
System.out.println("遍历表：");
System.out.println(list);
System.out.println("表长为："+list.size());
}
}
