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.

 /**
  * Definition for singly-linked list with a random pointer.
  * class RandomListNode {
  *     int label;
  *     RandomListNode next, random;
  *     RandomListNode(int x) { this.label = x; }
  * };
  */
 public class Solution {
     public RandomListNode copyRandomList(RandomListNode head) {
         if(head==null)
             return null;
         RandomListNode p=head;
//拷贝当前节点，并将其插入到被拷贝节点的后方
         while(p!=null){
             RandomListNode temp=new RandomListNode(p.label);
             temp.next=p.next;
             p.next=temp;
             p=temp.next;
         }
         p=head;
//将拷贝节点的随机指针指向应有位置
         while(p!=null){
             if(p.random!=null){
                 p.next.random=p.random.next;
             }
             p=p.next.next;
         }
         RandomListNode newhead=head.next;
         p=head;
//将拷贝链表与原链表分离
         while(p!=null){
             RandomListNode temp=p.next;
             p.next=temp.next;
             if(temp.next!=null)
                 temp.next=temp.next.next;
             p=p.next;
         }
         return newhead;
     }
 }

最后分离也可这样写：

 while(p != null && p.next != null){
     RandomListNode temp = p.next;
     p.next = temp.next;
     p = temp;
 }

解法2：

可以用hashmap的方式

 public RandomListNode copyRandomList(RandomListNode head) {
     if (head == null)
         return null;
     HashMap<RandomListNode, RandomListNode> map = new HashMap<RandomListNode, RandomListNode>();
     RandomListNode newHead = new RandomListNode(head.label);

     RandomListNode p = head;
     RandomListNode q = newHead;
     map.put(head, newHead);

     p = p.next;
     while (p != null) {
         RandomListNode temp = new RandomListNode(p.label);
         map.put(p, temp);
         q.next = temp;
         q = temp;
         p = p.next;
     }

     p = head;
     q = newHead;
     while (p != null) {
         if (p.random != null)
             q.random = map.get(p.random);
         else
             q.random = null;

         p = p.next;
         q = q.next;
     }

     return newHead;
 }