class Node{
    int value;
    Node next;
    Node rand;
    Node(int val){
        value = val;
    }
}

rand指针是单链表节点结构中新增的指针，rand可能指向链表中的任意一个节点，也可能指向null。
给定一个由Node节点类型组成的无环单链表的头节点head，请实现一个函数完成这个链表的复制，并返回复制的新链表的头节点。
【要求】时间复杂度0（N），额外空间复杂度0（1）

package Algorithms;

/**
 * @author : zhang
 * @version : 1.0
 * @date : Create in 2021/8/11
 * @description :
 */


import java.util.HashMap;

public class CopyListWithRandom {

    public static class Node {
        public int value;
        public Node next;
        public Node rand;

        public Node(int data) {
            this.value = data;
        }
    }

    //笔试  额外空间  哈希表
    public static Node copyListWithRand1(Node head) {
        HashMap<Node, Node> map = new HashMap<Node, Node>();
        Node cur = head;
        //1、循环往map中克隆Node，以老Node为key,value为对应copy的Node
        while (cur != null) {
            map.put(cur, new Node(cur.value));
            cur = cur.next;
        }
        cur = head;
        //2、处理next指针与rand指针
        while (cur != null) {
            //cur老   map.get(cur) 新
            //cur.next为链表中Node的下一个节点，
            //       找出来作为key，在map中查找的value就是新Node【map.get(cur).next)】的next所要指向的节点
            map.get(cur).next = map.get(cur.next);
            map.get(cur).rand = map.get(cur.rand);
            cur = cur.next;
        }
        return map.get(head);
    }

    //面试：不利用额外空间
    public static Node copyListWithRand2(Node head) {
        if (head == null) {
            return null;
        }
        Node cur = head;
        Node next = null;
        //1、 copy node and link to every node
        //例 【1 ->2 】 -> 【1 -> 1‘ -> 2 -> 2‘】
        while (cur != null) {
            next = cur.next; //next保存cur的下一个节点
            cur.next = new Node(cur.value); //cur的下一个Node指向新克隆的Node
            cur.next.next = next; //新克隆的Node的下一个节点指向next
            cur = next;//cur后移，然后重复以上操作
        }
        cur = head;
        Node curCopy = null;
        //2、 set copy node rand
        while (cur != null) {
            next = cur.next.next;
            curCopy = cur.next;
            curCopy.rand = cur.rand != null ? cur.rand.next : null;
            cur = next;
        }
        Node res = head.next;
        cur = head;
        //3、 split
        while (cur != null) {
            next = cur.next.next;
            curCopy = cur.next;
            cur.next = next;
            curCopy.next = next != null ? next.next : null;
            cur = next;
        }
        return res;
    }

    public static void printRandLinkedList(Node head) {
        Node cur = head;
        System.out.print("order: ");
        while (cur != null) {
            System.out.print(cur.value + " ");
            cur = cur.next;
        }
        System.out.println();
        cur = head;
        System.out.print("rand:  ");
        while (cur != null) {
            System.out.print(cur.rand == null ? "- " : cur.rand.value + " ");
            cur = cur.next;
        }
        System.out.println();
    }

    public static void main(String[] args) {
        Node head = new Node(1);
        head.next = new Node(2);
        head.next.next = new Node(3);
        head.next.next.next = new Node(4);
        head.next.next.next.next = new Node(5);
        head.next.next.next.next.next = new Node(6);

        head.rand = head.next.next.next.next.next; // 1 -> 6
        head.next.rand = head.next.next.next.next.next; // 2 -> 6
        head.next.next.rand = head.next.next.next.next; // 3 -> 5
        head.next.next.next.rand = head.next.next; // 4 -> 3
        head.next.next.next.next.rand = null; // 5 -> null
        head.next.next.next.next.next.rand = head.next.next.next; // 6 -> 4

        System.out.println("原链表为：");
        printRandLinkedList(head);
        Node res1 = copyListWithRand1(head);
        System.out.println("【方式1】copy的链表为：");
        printRandLinkedList(res1);
         Node res2 = copyListWithRand2(head);
        System.out.println("【方式2】copy的链表为：");
        printRandLinkedList(res2);
        System.out.println("原链表为：");
        printRandLinkedList(head);
    }
}

/**
 * 原链表为：
 * order: 1 2 3 4 5 6 
 * rand:  6 6 5 3 - 4 
 * 【方式1】copy的链表为：
 * order: 1 2 3 4 5 6 
 * rand:  6 6 5 3 - 4 
 * 【方式2】copy的链表为：
 * order: 1 2 3 4 5 6 
 * rand:  6 6 5 3 - 4 
 * 原链表为：
 * order: 1 2 3 4 5 6 
 * rand:  6 6 5 3 - 4 
 */