LeetCode – Copy List with Random Pointer

A linked list is given such that each node contains an additional random pointer which could point to any node in the list or null.

Return a deep copy of the list.

 1 /**
 2  * Definition for singly-linked list with a random pointer.
 3  * class RandomListNode {
 4  *     int label;
 5  *     RandomListNode next, random;
 6  *     RandomListNode(int x) { this.label = x; }
 7  * };
 8  */
 9 public class Solution {
10     public RandomListNode copyRandomList(RandomListNode head) {
11         if(head==null)
12             return null;
13         RandomListNode p=head;
//拷贝当前节点，并将其插入到被拷贝节点的后方
14         while(p!=null){
15             RandomListNode temp=new RandomListNode(p.label);
16             temp.next=p.next;
17             p.next=temp;
18             p=temp.next;
19         }
20         p=head;
//将拷贝节点的随机指针指向应有位置
21         while(p!=null){
22             if(p.random!=null){
23                 p.next.random=p.random.next;
24             }
25             p=p.next.next;
26         }
27         RandomListNode newhead=head.next;
28         p=head;
//将拷贝链表与原链表分离
29         while(p!=null){
30             RandomListNode temp=p.next;
31             p.next=temp.next;
32             if(temp.next!=null)
33                 temp.next=temp.next.next;
34             p=p.next;
35         }
36         return newhead;
37     }
38 }

最后分离也可这样写：

1 while(p != null && p.next != null){
2     RandomListNode temp = p.next;
3     p.next = temp.next;
4     p = temp;
5 }

解法2：

可以用hashmap的方式

 1 public RandomListNode copyRandomList(RandomListNode head) {
 2     if (head == null)
 3         return null;
 4     HashMap<RandomListNode, RandomListNode> map = new HashMap<RandomListNode, RandomListNode>();
 5     RandomListNode newHead = new RandomListNode(head.label);
 6  
 7     RandomListNode p = head;
 8     RandomListNode q = newHead;
 9     map.put(head, newHead);
10  
11     p = p.next;
12     while (p != null) {
13         RandomListNode temp = new RandomListNode(p.label);
14         map.put(p, temp);
15         q.next = temp;
16         q = temp;
17         p = p.next;
18     }
19  
20     p = head;
21     q = newHead;
22     while (p != null) {
23         if (p.random != null)
24             q.random = map.get(p.random);
25         else
26             q.random = null;
27  
28         p = p.next;
29         q = q.next;
30     }
31  
32     return newHead;
33 }