459. Repeated Substring Pattern

459. Repeated Substring Pattern

Easy

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.)

这道题的题意是让我们判断一个字符串是否能拆成多个子串，既然能拆成多个子串，那么每个子串的长度肯定不能大于字符串的一半。

1. 从字符串的一半开始遍历
2. 子串从 0 -> i 截取，然后将子串重复 len / i 次，构成新串
3. 判断和原来的字符串是否相等

Java

class Solution {
    public boolean repeatedSubstringPattern(String s) {
        int len = s.length();
        for(int i = 1; i <= len/2; i++){
            String sub = s.substring(0, i);
            StringBuffer sb = new StringBuffer();
            for(int j=0; j<len/i; j++){
                sb.append(sub);
            }
            if(sb.toString().equals(s)){
                return true;
            }
        }
        return false;
    }
}

Python

class Solution:
    def repeatedSubstringPattern(self, s: str) -> bool:
        len_ = len(s)
        for i in range(1, len_//2+1):
            if len_ % i == 0:
                sub_str = s[:i]
                if sub_str * (len_//i) == s:
                    return True
        return False