138. Copy List with Random Pointer

/**
 * 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) {
      RandomListNode dummy = new RandomListNode(0);
      RandomListNode cur = dummy;
      
      HashMap<RandomListNode, RandomListNode> map = new HashMap<>();
      while( head != null){
        if(!map.containsKey(head)){
          map.put( head, new RandomListNode(head.label));
        }
        cur.next = map.get(head);
        if(head.random!= null){
          if(!map.containsKey(head.random)){
            map.put(head.random, new RandomListNode(head.random.label));
          }
          cur.next.random = map.get(head.random);
        }
        cur = cur.next;
        head = head.next;
      }
      return dummy.next;
    }
}

 

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.