For two strings s and t, we say "t divides s" if and only if s = t + t + 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.
1 <= str1.length, str2.length <= 1000str1 and str2 consist of English uppercase letters.str1 = "ABCABC", str2 = "ABC""ABC"str1 = "ABABAB", str2 = "ABAB""AB"str1 = "LEET", str2 = "CODE"""