Problem URL: Greatest common divisor of strings

We will check if the length of str1 is divisible by the length of str2. If it is, we will check if str1 is equal to str2 multiplied by the length of str1 divided by the length of str2. If it is, we will return str2. Otherwise, we will return an empty string. If the length of str1 is not divisible by the length of str2, we will check if the length of str2 is divisible by the length of str1. If it is, we will check if str2 is equal to str1 multiplied by the length of str2 divided by the length of str1. If it is, we will return str1. Otherwise, we will return an empty string.

class Solution:
    def gcdOfStrings(self, str1: str, str2: str) -> str:
        if len(str1) % len(str2) == 0:
            if str1 == str2 * (len(str1) // len(str2)):
                return str2
            else:
                return ""
        elif len(str2) % len(str1) == 0:
            if str2 == str1 * (len(str2) // len(str1)):
                return str1
            else:
                return ""
        else:
            return ""

Time complexity: O(n)
Space complexity: O(1)

We can achieve the same thing using the math.gcd function.

class Solution:
    def gcdOfStrings(self, str1: str, str2: str) -> str:
        return str1[:math.gcd(len(str1), len(str2))] if str1+str2 == str2+str1 else ""