//跳跃表的实现
//元素有序且不重复
public class SkipList {private Node head;//顶层头节点    private int rate;//相邻两层元素个数的比例    private int level;//跳跃表层数    private int length;//底层节点个数    private int size;//所有层节点个数private final boolean order;//true表示正序，false表示逆序    private Random random;//随机数    private Stack<Node> stack;//保存查询时遍历的节点//节点类private static class Node {private Comparable comparable;private Node right;//同一层的右边节点private Node down;//下一层的对应节点public Node(Comparable comparable) {this.comparable = comparable;this.right = null;this.down = null;}}public SkipList(int rate, int level, boolean order) {this.rate = rate;this.level = level;this.length = 0;this.size = 0;this.order = order;this.random = new Random();this.stack = new Stack<Node>();this.head = new Node(null);//头节点的值默认为nullNode temp = head;for (int i = 1; i < level; i++) {temp.down = new Node(null);temp = temp.down;}}}

    //查询元素，自顶向下//正序时，返回底层【小于】给定值的最大的节点，包含头节点//逆序时，返回底层【大于】给定值的最小的节点，包含头节点private Node search(Comparable comparable) {stack.clear();Node temp = head;//从顶层开始while (true) {while (temp.right != null) {if (order && temp.right.comparable.compareTo(comparable) >= 0)//正序时查找当前层【小于】给定值的最大的节点break;if (!order && temp.right.comparable.compareTo(comparable) <= 0)//逆序时查找当前层【大于】给定值的最小的节点break;temp = temp.right;}if (temp.down == null)//找到底层的节点break;stack.push(temp);//stack保存遍历路径中每一层最右边的节点，除底层外temp = temp.down;//转到下一层}return temp;}

    //添加元素//若元素已存在，则返回，保证无重复元素public void insert(Comparable comparable) {Node temp = search(comparable);if (temp.right != null && temp.right.comparable.compareTo(comparable) == 0)//元素已存在return;Node node = new Node(comparable);Node other;//根据随机数，自底向上添加每层的新节点while (true) {node.right = temp.right;temp.right = node;//当前层添加完毕size++;if (random.nextInt(rate) != 0 || stack.isEmpty())break;//若随机数为0且还未到顶层，则向上层添加元素temp = stack.pop();other = node;node = new Node(comparable);node.down = other;}length++;return;}

    //删除元素//若元素不存在，则返回，否则删除所有层中包含的元素public void delete(Comparable comparable) {Node temp = search(comparable);if (temp.right == null || temp.right.comparable.compareTo(comparable) != 0)//元素不存在return;while (true) {if (temp.right == null || temp.right.comparable.compareTo(comparable) != 0) //当前层的元素不存在break;//从底层开始，依次删除每层的元素temp.right = temp.right.right;size--;if (stack.isEmpty())//到达顶层break;temp = stack.pop();//转到上一层}length--;return;}