跳表的由来及Java实现详解

public int getRandomLevel(){
        int level = 1;
        while(Math.random()<0.5&&level<MAX_LEVEL){
            level++;
        }
        return level;
    }

public class SkipNode<E> {
	private String key;
	private E value;
	/**
		数组存储每层索引的下一个节点。比如下标0表示链表本身，
		下标1表示第一层索引，依次类推。
	*/
	private SkipNode<E>[] next; 
	public SkipNode( String key, E value, int length ){
		this.key = key;
		this.value = value;
		next = new SkipNode[length];
	}
}

public class SkipList<E> {
    /**
    	maxLevel 索引最大高度
    	currentLevel 当前索引高度
    	head 跳表头节点，从head查起
    */
	private int maxLevel;
	private int currentLevel;
	private SkipNode head;
	public SkipList(int maxLevel, int currentLevel){
		this.maxLevel = maxlevel;
		this.currentLevel = currentLevel
		head = new SkipNode("head",null,maxLevel);
	}
}

public void insert( int key, E data ){
        SkipNode c = this.head;
        SkipNode[] update = new SkipNode[maxLevel];
        for( int i=currentLevel-1; i>=0; i--){
            while(c.next[i]!=null&&key>c.next[i].key){
                c=c.next[i];
            }
            if(c.key==key){
                c.data = data;
                return;
            }
            /**
            	记录每一层的入口节点，如果要插入索引下面会用到
            */
            update[i] = c;
        }
        int randomLevel = getRandomLevel();
        SkipNode newNode = new SkipNode(key,data,randomLevel);
        if(randomLevel>currentLevel){
            for( int i=currentLevel; i<randomLevel; i++ ){
                update[i]=this.head;
            }
            currentLevel = randomLevel;
        }
        /**
        	当前节点作为新索引节点，更新每一层的索引指向
        */
        for( int i=randomLevel-1; i>=0;i--){
            newNode.next[i] = update[i].next[i];
            update[i].next[i] = newNode;
        }
    }
    public E search( int key ){
        SkipNode<E> c = this.head;
        for( int i = currentLevel-1; i>=0; i-- ){
            while(c.next[i]!=null&&key> c.next[i].key){
                c=c.next[i];
            }
            if(c.next[i]!=null&&c.next[i].key==key){
                return c.next[i].data;
            }
        }
        return null;
    }
    public void delete( int key ){
        SkipNode skipNode = this.head;
        SkipNode[] delete = new SkipNode[currentLevel];
        for( int i=currentLevel-1; i>=0; i-- ){
            while( skipNode.next[i]!=null&&skipNode.next[i].key<key){
                skipNode = skipNode.next[i];
            }
            delete[i]=skipNode;
        }
if(delete[0].next[0]!=null&&delete[0].next[0].key==key){
            SkipNode deleteNode = delete[0].next[0];
            for( int i=0; i<currentLevel; i++ ){
                if(delete[i].next[i]==deleteNode){
                    delete[i].next[i] = delete[i].next[i].next[i];
                }
            }
      while(currentLevel>1&&this.head.next[currentLevel-1]==null){
                currentLevel--;
            }
        }
    }