129 lines
3.4 KiB
Java
129 lines
3.4 KiB
Java
package skiplist;
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/**
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* 跳表的一种实现方法。
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* 跳表中存储的是正整数，并且存储的是不重复的。
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*
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* Author：ZHENG
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*/
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public class SkipList {
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private static final float SKIPLIST_P = 0.5f;
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private static final int MAX_LEVEL = 16;
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private int levelCount = 1;
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private Node head = new Node(); // 带头链表
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public Node find(int value) {
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Node p = head;
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for (int i = levelCount - 1; i >= 0; --i) {
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while (p.forwards[i] != null && p.forwards[i].data < value) {
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p = p.forwards[i];
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}
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}
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if (p.forwards[0] != null && p.forwards[0].data == value) {
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return p.forwards[0];
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} else {
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return null;
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}
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}
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public void insert(int value) {
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int level = randomLevel();
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Node newNode = new Node();
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newNode.data = value;
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newNode.maxLevel = level;
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Node update[] = new Node[level];
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for (int i = 0; i < level; ++i) {
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update[i] = head;
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}
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// record every level largest value which smaller than insert value in update[]
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Node p = head;
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for (int i = level - 1; i >= 0; --i) {
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while (p.forwards[i] != null && p.forwards[i].data < value) {
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p = p.forwards[i];
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}
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update[i] = p;// use update save node in search path
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}
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// in search path node next node become new node forwords(next)
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for (int i = 0; i < level; ++i) {
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newNode.forwards[i] = update[i].forwards[i];
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update[i].forwards[i] = newNode;
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}
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// update node hight
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if (levelCount < level) levelCount = level;
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}
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public void delete(int value) {
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Node[] update = new Node[levelCount];
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Node p = head;
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for (int i = levelCount - 1; i >= 0; --i) {
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while (p.forwards[i] != null && p.forwards[i].data < value) {
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p = p.forwards[i];
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}
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update[i] = p;
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}
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if (p.forwards[0] != null && p.forwards[0].data == value) {
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for (int i = levelCount - 1; i >= 0; --i) {
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if (update[i].forwards[i] != null && update[i].forwards[i].data == value) {
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update[i].forwards[i] = update[i].forwards[i].forwards[i];
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}
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}
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}
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while (levelCount>1&&head.forwards[levelCount]==null){
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levelCount--;
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}
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}
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// 理论来讲，一级索引中元素个数应该占原始数据的 50%，二级索引中元素个数占 25%，三级索引12.5% ，一直到最顶层。
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// 因为这里每一层的晋升概率是 50%。对于每一个新插入的节点，都需要调用 randomLevel 生成一个合理的层数。
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// 该 randomLevel 方法会随机生成 1~MAX_LEVEL 之间的数，且 ：
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// 50%的概率返回 1
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// 25%的概率返回 2
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// 12.5%的概率返回 3 ...
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private int randomLevel() {
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int level = 1;
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while (Math.random() < SKIPLIST_P && level < MAX_LEVEL)
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level += 1;
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return level;
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}
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public void printAll() {
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Node p = head;
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while (p.forwards[0] != null) {
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System.out.print(p.forwards[0] + " ");
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p = p.forwards[0];
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}
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System.out.println();
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}
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public class Node {
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private int data = -1;
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private Node forwards[] = new Node[MAX_LEVEL];
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private int maxLevel = 0;
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@Override
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public String toString() {
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StringBuilder builder = new StringBuilder();
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builder.append("{ data: ");
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builder.append(data);
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builder.append("; levels: ");
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builder.append(maxLevel);
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builder.append(" }");
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return builder.toString();
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}
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}
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}
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