leetcode_gym/_problems/copyListWithRandomPointer.md

layout, title, last_solved, category, leetcode_url, status

layout	title	last_solved	category	leetcode_url	status
page	Copy List with Random Pointer		linked list	https://leetcode.com/problems/copy-list-with-random-pointer/	Attempted

Problem

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.

Solution

It's trivial to clone the linked list but not with the random pointer. The random pointer would point to a node that hasn't been cloned yet.

1. Go thru list and build a hashmap with K=original node and V=cloned node
2. Go thru the list again and wire up the next and random cloned nodes

This has a bug and haven't been able to figure it out.

{% highlight python %}

from collections import defaultdict

class Solution: def copyRandomList(self, head: 'Node') -> 'Node':

    curr = head
    mapping = defaultdict(Node)
    
    # go thru list once and just create nodes and add to mapping
    while curr:
        
        # create new node
        newNode = Node(curr.val, None, None)
        
        # add to map
        mapping[curr] = newNode
        
        # move to next node
        curr = curr.next
    
    
    # go thru list again and wire up the next and random pointers
    curr = head
    
    while curr:
        
        # get cloned node
        clonedCurr = mapping[curr]
        
        # get next and random of original node
        origNext = curr.next
        origRandom = curr.random
        
        # get cloned version of orig next and random
        clonedNext = mapping.get(origNext, None)
        clonedRandom = mapping.get(origRandom, None)
        
        # print(clonedCurr.val)
        # print(clonedNext.val)
        # print()
        # print(clonedCurr.val, origNext.val, clonedNext.val)
        
        # wire up cloned nodes
        clonedCurr.next = clonedNext
        clonedCurr.next = clonedRandom
        
        
        # move to next node
        curr = curr.next
        
    
    return mapping[head]

{% endhighlight %}

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{% highlight python %}

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