Add Two Numbers as Lists

Problem

Add two non-negative integers whose digits are stored as linked lists in least-significant-first order.

a and b are lists of decimal digits with the ones digit first. Walk both lists with a carry and append sum % 10 at each step, continuing while any digits or carry remain.

Return the sum as a digit list in the same least-significant-first order.

Hint

Process one digit per list per step and keep the carry until both lists and the carry are exhausted.

Test cases

case 1

in: [[2,4,3],[5,6,4]]

expected: [7,0,8]

case 2

in: [[0],[0]]

expected: [0]

case 3

in: [[9,9],[1]]

expected: [0,0,1]

case 4

in: [[9],[9]]

expected: [8,1]

case 5

in: [[1,8],[0]]

expected: [1,8]

Starter codePython

def add_two_numbers(a, b):
    # Your code here
    pass

5 test cases · run your code against them in the editor