Good evening! Here's our prompt for today.

We're provided the following two linked lists:

1 -> 2 -> 3 -> 4 and 2 -> 5 -> 8

Each one represents a number in reversed order, so 1 -> 2 -> 3 -> 4 represents 4321 and 2 -> 5 -> 8 represents 852 (note: for an extra challenge, consider if they weren't reversed).

The lists are guaranteed to have at least one node and will not have any leading 0s. Each of the nodes contain a single digit.

Can you write a method to add the two numbers and return it as another linked list?

1// list1: 1 -> 2 -> 3 ->4
2// list2: 2 -> 5 -> 8
3
4addLLNums(list1, list2);
5// should return 3 -> 7 -> 1 -> 5
6// 4321 + 852 = 5173

Constraints

• Length of both linked lists list1, list2 <= 100000
• Value stored in each node is between 0 and 9
• Make sure that you have to return a linked list and not a number
• Expected time complexity : O(n)
• Expected space complexity : O(n)

Try to solve this here or in Interactive Mode.

How do I practice this challenge?

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# function to add the numbers of two linked list

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def add_numbers(list1, list2):

    # fill in this method

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    return list1

​

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class Node:

    def __init__(self, val):

        self.val = val

        self.next = None

​

​

class LinkedList:

    def __init__(self):

        self.head = None

​

    # function to insert the node at the beginning

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    def push(self, value):

        node = Node(value)

        node.next = self.head

        self.head = node

​

    # Utility function to print the linked LinkedList

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    def printList(self):

Here's our guided, illustrated walk-through.

How do I use this guide?