1206. 设计跳表

不使用任何库函数，设计一个 跳表 。

class Skiplist {
 
    int level=0;
 
    Node head=null;
 
    public Skiplist() {
 
    }
    
    public boolean search(int target) {
        Node cur=head;
        while(cur!=null){
            while(cur.right!=null&&cur.right.val
                cur=cur.right;
            }
            if(cur.right!=null&&cur.right.val==target){
                return true;
            }
            cur=cur.down;
        }
        return false;
    }
    
    public void add(int num) {
        int rLevel=1;
        while(rLevel<=level&&(Math.random()%2)==1){
            rLevel++; // 2
        }
        if(rLevel>level){
            level=rLevel;
            head=new Node(num,null,head);
        }
        Node cur=head,last=null;
        for(int l=level;l>0;l--){
            while(cur.right!=null&&cur.right.val
                cur=cur.right;
            }
            if(l<=rLevel){
                cur.right=new Node(num,cur.right,null);
                if(last!=null){
                    last.down=cur.right;
                }
                last=cur.right;
            }
            cur=cur.down;
        }
    }
    // 擦除
    public boolean erase(int num) {
        Node cur=head;
        boolean seen=false;
        for(int l=level;l>0;l--){
            while(cur.right!=null&&cur.right.val
                cur=cur.right;
            }
            if(cur.right!=null&&cur.right.val==num){
                seen=true;
                // Node tmp=cur.right;
                cur.right=cur.right.right;
            }
            cur=cur.down;
        }
        return seen;
    }
}
 
/**
 * Your Skiplist object will be instantiated and called as such:
 * Skiplist obj = new Skiplist();
 * boolean param_1 = obj.search(target);
 * obj.add(num);
 * boolean param_3 = obj.erase(num);
 */
 
public class Node {
    public int val;
    public Node right,down;
 
    Node() {
    }
 
    public Node(int val) {
        this.val = val;
    }
 
    Node(int val, Node right,Node down) {
        this.val = val;
        this.right = right;
        this.down = down;
    }
 
    /*public void add(int value) {
        Node p = this;
        while (p.right != null) {
            p = p.right;
        }
        Node newNode = new Node(value);
        p.right = newNode;
    }
    public void add(Node node) {
        Node p = this;
        while (p.right != null) {
            p = p.right;
        }
        p.right = node;
    }*/
}