Greatest Common Divisor of Strings — LeetCode 1071 Python Solution

The problem

For two strings s and t, we say "t divides s" if and only if s = t + t + t + ... + t + t (i.e., t is concatenated with itself one or more times).

Python solution

class Solution:
    def gcdOfStrings(self, str1: str, str2: str) -> str:
        def check(a, b):
            c = ""
            while len(c) < len(b):
                c += a
            return c == b

        for i in range(min(len(str1), len(str2)), 0, -1):
            t = str1[:i]
            if check(t, str1) and check(t, str2):
                return t
        return ''

Complexity

Pattern: Math and Number Theory

Find the closed form, the invariant, or the modular identity — and skip the loop entirely. LeetCode 1071. Greatest Common Divisor of Strings is filed here on both counts: the reference solution below belongs to the algorithm family this hub collects, and LeetCode tags it Math.

The math and number theory guide has the Python template for the pattern and the 485 LeetCode problems that use it.

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