Leetcode 138: 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.

 

/**
 * Definition for singly-linked list with a random pointer.
 * public class RandomListNode {
 *     public int label;
 *     public RandomListNode next, random;
 *     public RandomListNode(int x) { this.label = x; }
 * };
 */
public class Solution {
    public RandomListNode CopyRandomList(RandomListNode head) {
        if (head == null) return null;
        
        RandomListNode newHead = new RandomListNode(head.label), cur = head, newCur = newHead;
        
        var dict = new Dictionary<RandomListNode, RandomListNode>();
        dict[head] = newHead;
        
        while (cur.next != null)
        {
            var n = new RandomListNode(cur.next.label);
            dict[cur.next] = n;
            newCur.next = n;
            cur = cur.next;
            newCur = newCur.next;
        }
        
        cur = head;
        newCur = newHead;
        
        while (cur != null)
        {
            if (cur.random != null && dict.ContainsKey(cur.random))
            {
                newCur.random = dict[cur.random];
            }
            
            cur = cur.next;
            newCur = newCur.next;
        }
        
        return newHead;
    }
}