Copy List with Random Pointer (138)

Screen Shot 2017-09-13 at 17.13.42.png

/**
 * 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 head;
        RandomListNode dummy = new RandomListNode(0);
        RandomListNode ptr = dummy;
        dummy.next = head;
        while(ptr.next != null)
        {
            RandomListNode next = ptr.next.next;
            ptr.next.next = new RandomListNode(ptr.next.label);
            ptr = ptr.next.next;
            ptr.next = next;
        }
        ptr = dummy;
        while(ptr.next != null)
        {
            if(ptr.next.random != null) ptr.next.next.random = ptr.next.random.next;
            ptr = ptr.next.next;
        }
        RandomListNode newdummy = new RandomListNode(0);
        RandomListNode newptr = newdummy;
        ptr = dummy;
        while(ptr.next != null)
        {
            newptr.next = ptr.next.next;
            newptr = newptr.next;
            ptr.next.next = ptr.next.next.next;
            ptr = ptr.next;
        }
        return newdummy.next;
    }
}