1071. Greatest Common Divisor of Strings

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

Constraints:

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