Add Strings

Problem

Add two non-negative integers given as decimal strings and return their sum as a decimal string, without converting the inputs to integers.

Walk both strings from the right, summing digits plus a carry and emitting the result digit. Any remaining carry becomes a final leading 1.

Hint

Build the result in reverse and flip it at the end; do not forget the final carry.

case 1

in: ["11","123"]

expected: "134"

case 2

in: ["0","0"]

expected: "0"

case 3

in: ["999","1"]

expected: "1000"

case 4

in: ["1","9"]

expected: "10"

case 5

in: ["456","77"]

expected: "533"

Starter codePython

def add_strings(num1, num2):
    # Your code here
    pass

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