Add Numbers via Linked Lists | Dataford Interview Questions

Add two numbers represented by linked lists.

Asked in the Technical interview 1 stage. Pseudocode first, then code; optimal solution expected.

Implement add_two_numbers(l1, l2). Each linked list stores one digit per node in reverse order, so the head contains the units digit. Return the head of a new linked list representing the sum in the same format. Do not convert the lists into whole integers.

Input and Output

l1 and l2 are linked-list heads containing digits from 0 to 9. Return a linked-list head containing the sum.

Constraints

Each linked list contains 1 to 1,000 nodes.
Each node value is an integer from 0 to 9.
The input lists represent non-negative integers.
Leading zeroes may occur.

Function Signature

def add_two_numbers(l1, l2):

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