LeetCode 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.)

【题目分析】

判断一个字符串是否是由某个子串重复多次构成。

【思路】

1. 子串至少重复两次

2. 从字符串的头部取长度范围为1~str.length()/2的子串，用正则表达式来进行判断。

【java代码】

public class Solution {
    public boolean repeatedSubstringPattern(String str) {
        if(str == null || str.length() < 2) return false;
        
        boolean result = false;
        for(int i = 1; i <= str.length()/2; i++) {
            if(str.length()%i != 0) continue;
            String regex = "("+str.substring(0,i)+")" + "+";
            result = result | str.matches(regex);
        }
        return result;
    }
}