For two strings s and t, we say "t divides s" if and only if s = t + ... + t  (t concatenated with itself 1 or more times)
Given two strings str1 and str2, return the largest string x such that x divides both str1 and str2.
 
Example 1:
Input: str1 = "ABCABC", str2 = "ABC"
Output: "ABC"
Example 2:
Input: str1 = "ABABAB", str2 = "ABAB"
Output: "AB"
Example 3:
Input: str1 = "LEET", str2 = "CODE"
Output: ""
Example 4:
Input: str1 = "ABCDEF", str2 = "ABC"
Output: ""

 
Constraints:

1 <= str1.length <= 1000
1 <= str2.length <= 1000
str1 and str2 consist of English uppercase letters.

Difficulty: introductory

Starter code:

class Solution:
    def gcdOfStrings(self, str1: str, str2: str) -> str:
        

Solutions:
class Solution:
    def gcdOfStrings(self, str1: str, str2: str) -> str:
        contender = ''
        for i in str1:
            contender += i
            if str1.count(contender) * len(contender) == len(str1) and str2.count(contender) * len(contender) == len(str2):
                break
        orig = contender
        ans = None
        while len(contender) <= len(str1) and len(contender) <= len(str2):
            t1 = str1.replace(contender, '')
            t2 = str2.replace(contender, '')
            if len(t1) == len(t2) == 0:
                ans = contender
            contender += orig
        return ans if ans else ''

class Solution:
    def gcdOfStrings(self, str1: str, str2: str) -> str:
        m, n = len(str1), len(str2)
        candidate, curr = '', ''
        
        for i in range(min(m, n)):
            if str1[i] != str2[i]:
                break
            else:
                curr += str1[i]
                if m % len(curr) == 0 and n % len(curr) == 0:
                    if str1 == curr * (m // len(curr)) and str2 == curr * (n // len(curr)):
                        candidate = curr
        
        return candidate


class Solution:
    def gcdOfStrings(self, str1: str, str2: str) -> str:
        def diviser(n):
            if n == 4:
                return [1,2]
            Result = [1]
            for i in range(2,n//2):
                if n%i == 0:
                    Result.extend([int(i),int(n/i)])
            return Result
        
        def str_diviser(str3):
            Result = ['',str3]
            Result1 = diviser(len(str3))
            if len(Result1) > 0:
                for i in Result1:
                    div=str3[:i]
                    for j in range(i,len(str3),i):
                        if str3[j:(j+i)] != div:
                            break
                        if j == len(str3)-i:
                            Result.append(div)
            return Result
        a=str_diviser(str1)
        b=str_diviser(str2)
        if len(a)>len(b):
            a,b = b,a
        Cur = ''
        for i in a:
            if i in b and len(i)>len(Cur):
                Cur = i
        return Cur