Python Program For Cloning A Linked List With Next And Random Pointer- Set 2

We have already discussed 2 different ways to clone a linked list. In this post, one more simple method to clone a linked list is discussed.

The idea is to use Hashing. Below is algorithm. 

1. Traverse the original linked list and make a copy in terms of data.
2. Make a hash map of key value pair with original linked list node and copied linked list node.
3. Traverse the original linked list again and using the hash map adjust the next and random reference of cloned linked list nodes.

Below is the implementation of above approach.

Python3

# Python3 program to clone a linked list
# with random pointers
class Node:
    def __init__(self, data):

        # Node Data
        self.data = data

        # Node Next
        self.next = None

        # Node Random
        self.random = None

# Dictionary
class MyDictionary(dict):

    # __init__ function
    def __init__(self):

        super().__init__()
        self = dict()

        # Function to add key:value
        def add(self, key, value):

        # Adding Values to dictionary
        self[key] = value

# Linked list class
class LinkedList:

    # Linked list constructor
    def __init__(self, node):
        self.head = node

    # Method to print the list.
    def __repr__(self):

        temp = self.head
        while temp is not None:
            random = temp.random
            random_data = (random.data if
                           random is not None else -1)

            data = temp.data
            print(f"Data-{data},
                  Random data: {random_data}")
            temp = temp.next

        return ""

    # Push method to put data always at
    # the head in the linked list.
    def push(self, data):

        node = Node(data)
        node.next = self.head
        self.head = node

    # Actual clone method which returns head
    # reference of cloned linked list.
    def clone(self):

        # Initialize two references, one
        # with original list's head.
        original = self.head
        clone = None

        # Initialize two references, one
        # with original list's head.
        mp = MyDictionary()

        # Traverse the original list and
        # make a copy of that
        # in the clone linked list
        while original is not None:
            clone = Node(original.data)
            mp.add(original, clone)
            original = original.next

        # Adjusting the original
        # list reference again.
        original = self.head

        # Traversal of original list again
        # to adjust the next and random
        # references of clone list using hash map.
        while original is not None:
            clone = mp.get(original)
            clone.next = mp.get(original.next)
            clone.random = mp.get(original.random)
            original = original.next

        # Return the head reference of the clone list.
        return LinkedList(self.head)

# Driver code

# Pushing data in the linked list.
l = LinkedList(Node(5))
l.push(4)
l.push(3)
l.push(2)
l.push(1)

# Setting up random references.
l.head.random = l.head.next.next
l.head.next.random =
l.head.next.next.next
l.head.next.next.random =
l.head.next.next.next.next
l.head.next.next.next.random =
(l.head.next.next.next.next.next)
l.head.next.next.next.next.random =
l.head.next

# Making a clone of the
# original linked list.
clone = l.clone()

# Print the original and cloned
# linked list.s
print("Original linked list")
print(l)
print("Cloned linked list")
print(clone)
# This code is contributed by ashwinathappan

Output:

Original linked list
Data = 1, Random data = 3
Data = 2, Random data = 4
Data = 3, Random data = 5
Data = 4, Random data = -1
Data = 5, Random data = 2

Cloned linked list
Data = 1, Random data = 3
Data = 2, Random data = 4
Data = 3, Random data = 5
Data = 4, Random data = -1
Data = 5, Random data = 2

Time complexity: O(n) 
Auxiliary space: O(n)
Please refer complete article on Clone a linked list with next and random pointer | Set 2 for more details!