Solution.java

/**
 * 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;
        }
        
        // step1
        RandomListNode cur = head;
        while (cur != null) {
            RandomListNode node = new RandomListNode(cur.label);
            node.next = cur.next;
            cur.next = node;
            cur = node.next;
        }
        
        // step2
        cur = head;
        while (cur != null) {
            RandomListNode clone = cur.next;
            if (cur.random != null) {
                clone.random = cur.random.next;   
            }
            cur = clone.next;
        }
        
        // step3
        cur = head;
        RandomListNode cloneHead = head.next;
        while (cur.next != null) {
            RandomListNode clone = cur.next;
            cur.next = clone.next;
            cur = clone;
        }
        
        return cloneHead;
    }
}