LeetCode 75 - 1071. Greatest Common Divisor of Strings

Description

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:
1 2
Input: str1 = "ABCABC", str2 = "ABC" Output: "ABC"
Example 2:
1 2
Input: str1 = "ABABAB", str2 = "ABAB" Output: "AB"
Example 3:
1 2
Input: str1 = "LEET", str2 = "CODE" Output: ""
Constraints:
- 1 <= str1.length, str2.length <= 1000
- str1 and str2 consist of English uppercase letters.

Solutions

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class Solution {
    bool check(string t,string s){
        int lenx = (int)s.length() / (int)t.length();
        string ans = "";
        for (int i = 1; i <= lenx; ++i){
            ans = ans + t;
        }
        return ans == s;
    }
public:
    string gcdOfStrings(string str1, string str2) {
        int len1 = (int)str1.length(), len2 = (int)str2.length();
        for (int i = min(len1, len2); i >= 1; --i){ // 从长度大的开始枚举
            if (len1 % i == 0 && len2 % i == 0){
                string X = str1.substr(0, i);
                if (check(X, str1) && check(X, str2)) return X;
            }
        }
        return "";
    }
};