Java利用跳跃表解决双重队列问题详解

package com.platform.modules.alg.alglib.poj3481;
 
import java.util.Random;
 
public class Poj3481D {
    private int INF = 0x7fffffff;
    private int MAX_LEVEL = 16;
    public String output = "";
 
    public String cal(String input) {
        Init();
        int op, num, val;
        String[] line = input.split("\n");
        int count = 0;
        while (true) {
            String commad[] = line[count++].split(" ");
            op = Integer.parseInt(commad[0]);
            if (op == 1) {
                num = Integer.parseInt(commad[1]);
                val = Integer.parseInt(commad[2]);
                Insert(num, val);
            } else if (op == 0) {
                return output;
            } else if (op == 2)
                Delete(true);
            else
                Delete(false);
        }
    }
 
    class Node {
        int num, val;
        Node forward[] = new Node[MAX_LEVEL];
    }
 
    public Poj3481D() {
        for (int i = 0; i < updata.length; i++) {
            updata[i] = new Node();
        }
    }
 
    Node head;
    Node updata[] = new Node[MAX_LEVEL];
 
    int level, max_k, min_k;
 
    void Init() {
        level = 0;
        max_k = -INF;
        min_k = INF;
        head = new Node();
        for (int i = 0; i < MAX_LEVEL; i++)
            head.forward[i] = null;
        head.val = -INF;
    }
 
    // 按规则选择数据应该在哪层插入
    int RandomLevel() {
        int lay = 0;
        while (new Random().nextInt(100) % 2 == 0 && lay < MAX_LEVEL - 1)
            lay++;
        return lay;
    }
 
    // 查找最接近val的元素
    Node Find(int val) {
        Node p = head;
        for (int i = level; i >= 0; i--) {
            while (p.forward[i] != null && p.forward[i].val < val)
                p = p.forward[i];
            updata[i] = p; // 记录搜索过程中各级走过的最大节点位置
        }
        return p;
    }
 
    void Insert(int num, int val) {
        if (val > max_k) max_k = val;
        if (val < min_k) min_k = val;
        Node s;
        int lay = RandomLevel();
        if (lay > level) // 要插入的层 > 现有层数
            level = lay;
        Find(val); //查询
        s = new Node(); // 创建一个新节点
        s.num = num;
        s.val = val;
        for (int i = 0; i < MAX_LEVEL; i++)
            s.forward[i] = null;
        for (int i = 0; i <= lay; i++) { // 插入操作
            s.forward[i] = updata[i].forward[i];
            updata[i].forward[i] = s;
        }
    }
 
    // flag=false 表示删除最小值，true 表示删除最大值
    void Delete(boolean flag) {
        int d;
        if (flag) d = max_k;
        else d = min_k;
        if (d == -INF || d == INF) { // 说明还没有插入元素
            output += "0\n";
            return;
        }
        Node p = Find(d);
        if (p.forward[0] != null && p.forward[0].val == d) {
            output += String.format("%d\n", p.forward[0].num);
 
            if (p.val == -INF && p.forward[0].forward[0] == null) // 删除唯一节点
            {
                max_k = -INF;
                min_k = INF;
            } else {
                if (flag) max_k = p.val;
                else min_k = p.forward[0].forward[0].val;
            }
            for (int i = level; i >= 0; i--) { // 删除操作
                if (updata[i].forward[i] != null && updata[i].forward[i].val == d)
                    updata[i].forward[i] = updata[i].forward[i].forward[i];
            }
        }
    }
}