459. Repeated Substring Pattern

Given a non-empty string check if it can be constructed by taking a substring of it and appending multiple copies of the substring together. You may assume the given string consists of lowercase English letters only and its length will not exceed 10000.
 
Example 1:
Input: "abab"
Output: True
Explanation: It's the substring "ab" twice.
Example 2:
Input: "aba"
Output: False
Example 3:
Input: "abcabcabcabc"
Output: True
Explanation: It's the substring "abc" four times. (And the substring "abcabc" twice.)

Input:
"bb"
Output:
false
Expected:
true


// passed 117/120 cases 
class Solution {
    public boolean repeatedSubstringPattern(String s) {
        // 2 parts , 3 parts, ... at most s.length / 2 parts 
        // get the substring , append it n times , check if same as string s
        // string.equals(), char use == 
        
        for(int i = 2; i <= s.length() / 2; i++){
            if(s.length() % i == 0){
                String sub = s.substring(0, s.length() / i);
                StringBuilder sb = new StringBuilder();
                for(int j = 0; j < i; j++){
                    sb.append(sub);
                }
                if(sb.toString().equals(s)) return true;
            }
        }
        return false;
        
    }
}


// correct , covered all the cases 
class Solution {
    public boolean repeatedSubstringPattern(String s) {
        // 2 parts , 3 parts, ... at most s.length / 2 parts 
        // get the substring , append it n times , check if same as string s
        // string.equals(), char use == 
        int l = s.length();
        for(int i = l / 2; i >= 1; i--){ // the length of each part 
            if(l % i == 0){ // if the part is divisible
                int m = l / i; // how many parts 
                String substring = s.substring(0, i);
                StringBuilder sb = new StringBuilder();
                for(int j = 0; j < m; j++){
                    sb.append(substring);
                }
                if(sb.toString().equals(s)) return true;
            }
        }
        return false;
    }
}