复制含有随机指针节点的链表

【题目】 一种特殊的链表节点类描述如下：
public class Node {
     public int value;
     public Node next;
     public Node rand;
    public Node(int data) {
         this.value = data;
    }
}
Node类中的value是节点值，next指针和正常单链表中next指针的意义
一 样，都指向下一个节点，rand指针是Node类中新增的指针，这个指
针可 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
这个链表中所有结构的复制，并返回复制的新链表的头节点。 进阶：
不使用额外的数据结构，只用有限几个变量，且在时间复杂度为 O(N)
内完成原问题要实现的函数。import java.util.HashMap;

public class C09 {
public static class Node {
public int value;//节点的值
public Node next;//下一节点
public Node rand;//任意一个节点

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

public static Node copyListWithRand1(Node head) {
HashMap<Node, Node> map = new HashMap<Node, Node>();
Node cur = head;//cur头节点，用于遍历链表
while (cur != null) {//遍历链表
map.put(cur, new Node(cur.value));//（原链表节点，副节点）
cur = cur.next;//指向下一个节点
}
cur = head;
while (cur != null) {
map.get(cur).next = map.get(cur.next);
map.get(cur).rand = map.get(cur.rand);
cur = cur.next;
}
return map.get(head);
}

public static Node copyListWithRand2(Node head) {
if (head == null) {
return null;
}
Node cur = head;
Node next = null;
// copy node and link to every node
while (cur != null) {
next = cur.next;
cur.next = new Node(cur.value);
cur.next.next = next;
cur = next;
}
cur = head;
Node curCopy = null;
// 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;
// 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 = null;
Node res1 = null;
Node res2 = null;
printRandLinkedList(head);
res1 = copyListWithRand1(head);
printRandLinkedList(res1);
res2 = copyListWithRand2(head);
printRandLinkedList(res2);
printRandLinkedList(head);
System.out.println("=========================");

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

printRandLinkedList(head);
res1 = copyListWithRand1(head);
printRandLinkedList(res1);
res2 = copyListWithRand2(head);
printRandLinkedList(res2);
printRandLinkedList(head);
System.out.println("=========================");

}
}