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.

The Linked List is represented in the input/output as a list of n nodes. Each node is represented as a pair of [val, random_index] where:

• val: an integer representing Node.val

• random_index: the index of the node (range from 0 to n-1) where random pointer points to, or null if it does not point to any node.

Example 1:

Input: head = [[7,null],[13,0],[11,4],[10,2],[1,0]]
Output: [[7,null],[13,0],[11,4],[10,2],[1,0]]

Example 2:

Input: head = [[1,1],[2,1]]
Output: [[1,1],[2,1]]

Example 3:

Input: head = [[3,null],[3,0],[3,null]]
Output: [[3,null],[3,0],[3,null]]

Example 4:

Input: head = []
Output: []
Explanation: Given linked list is empty (null pointer), so return null.

Constraints:

• -10000 <= Node.val <= 10000

• Node.random is null or pointing to a node in the linked list.

• Number of Nodes will not exceed 1000.

/*
// Definition for a Node.
class Node {
    int val;
    Node next;
    Node random;

    public Node(int val) {
        this.val = val;
        this.next = null;
        this.random = null;
    }
}
*/
// O(n) -> time && O(n) -> space.
class Solution {
    public Node copyRandomList(Node head) {
        HashMap<Node, Node> map = new HashMap<>();
        Node current = head;
        while (current != null) {
            Node temp = new Node(current.val);
            map.put(current, temp);
            current = current.next;
        }
        Node ans = map.get(head);
        current = head;
        while (current != null) {
            Node temp = map.get(current);
            if (current.next != null)
                temp.next = map.get(current.next);
            if (current.random != null) {
                temp.random = map.get(current.random);
            }
            current = current.next;
        }
        return ans;
    }
}
//O(n) -> time and O(1) ->Space.
class Solution {
    public Node copyRandomList(Node head) {
        if(head==null)
            return null;
        Node current = head;
        while (current != null) {
            Node copy = new Node(current.val);
            copy.next = current.next;
            current.next = copy;
            current = copy.next;
        }
        current = head;
        Node ans = head.next;
        while (current != null) {
            Node copy = current.next;
            if (current.random != null)
                copy.random = current.random.next;
            current = copy.next;
        }
        current = head;
        while (current != null) {
            Node copy = current.next;
            if (copy.next != null) {
                current.next = copy.next;
                copy.next = copy.next.next;
            } else {
                current.next = copy.next;
            }
            current = current.next;
        }
        return ans;
    }
}