Copy List

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.

Given list

   1 -> 2 -> 3

with random pointers going from

  1 -> 3
  2 -> 1
  3 -> 1

You should return a deep copy of the list. The returned answer should not contain the same node as the original list, but a copy of them. The pointers in the returned list should not link to any node in the original input list.


Solution:

Time: O(n)
Space: O(n)

/**
 * 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) {
        Map<RandomListNode, RandomListNode> map = new HashMap<>();
        RandomListNode p = head;
        RandomListNode dummy = new RandomListNode(0);
        RandomListNode n = dummy;
        while (p != null) {
            RandomListNode r = map.getOrDefault(p, new RandomListNode(p.label));
            map.put(p, r);
            if (p.random != null) {
                r.random = map.getOrDefault(p.random, new RandomListNode(p.random.label));
                map.put(p.random, r.random);
            }
            n.next = r;
            n = n.next;
            p = p.next;
        }
        return dummy.next;
    }
}