class Solution {
public:
    string gcdOfStrings(string str1, string str2) {
        return (str1 + str2 == str2 + str1)?  // if adding str2 to the start is the same as adding it to the end (if they're the same it's just repeated same thing) == true then
        str1.substr(0, gcd(size(str1),size(str2))) // whats being returned = SUBSTRING starting from 0 to the gcd ( COMMON DIVISOR FOR ) the size of str1 and str2
        : ""; // else return nothing
    }
};