_138.java

package com.fishercoder.solutions;

import java.util.HashMap;
import java.util.Map;

/**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.*/

public class _138 {

    public RandomListNode copyRandomList(RandomListNode head) {
        Map<RandomListNode, RandomListNode> map = new HashMap();
        RandomListNode node = head;

        //loop for the first time: copy the node themselves
        while(node != null){
            map.put(node, new RandomListNode(node.label));
            node = node.next;
        }
        
        //loop for the second time: copy random and next pointers
        node = head;
        while(node != null){
            map.get(node).next = map.get(node.next);
            map.get(node).random = map.get(node.random);
            node = node.next;
        }
        
        return map.get(head);
    }
}

// Definition for singly-linked list with a random pointer.
class RandomListNode {
     int label;
     RandomListNode next, random;
     RandomListNode(int x) { this.label = x; }
 }