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.

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/**
 * 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 newHead = new RandomListNode(0);
        Map<RandomListNode, RandomListNode> oldToNew = new HashMap<RandomListNode, RandomListNode>();
        Map<RandomListNode, RandomListNode> newToOld = new HashMap<RandomListNode, RandomListNode>();
        if(head != null){
            RandomListNode nextNode = head;
            RandomListNode nextNewNode = newHead;
            while(nextNode != null){
                nextNewNode.next = new RandomListNode(nextNode.label);
                nextNewNode = nextNewNode.next;
                oldToNew.put(nextNode, nextNewNode);
                newToOld.put(nextNewNode, nextNode);
                nextNode = nextNode.next;
            }
            nextNewNode.next = null;
            nextNewNode = newHead.next;
            while(nextNewNode != null){
                RandomListNode tempOld = newToOld.get(nextNewNode);
                RandomListNode tempnew = oldToNew.get(tempOld.random);
                nextNewNode.random = tempnew;
                nextNewNode = nextNewNode.next;
            }
        }
        newHead = newHead.next;
        return newHead;
    }
}