Leetcode: 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.)

这道题应该没法用DP等解，只能brute force 或者 KMP（为深究）

BruteForce, Best Solution for now except KMP

public boolean repeatedSubstringPattern(String str) {
    int l = str.length();
    for(int i=l/2;i>=1;i--) {
        if(l%i==0) {
            int m = l/i;
            String subS = str.substring(0,i);
            StringBuilder sb = new StringBuilder();
            for(int j=0;j<m;j++) {
                sb.append(subS);
            }
            if(sb.toString().equals(str)) return true;
        }
    }
    return false;
}

作为Encode String with Shortest Length的subproblem

public class Solution {
    public boolean repeatedSubstringPattern(String str) {
        int len = str.length();
        for (int i=len/2; i>0; i--) {
            if (len%i == 0) {
                String substr = str.substring(0, i);
                if (str.replaceAll(substr, "").length() == 0) 
                    return true;
            }
        }
        return false;
    }
}

KMP解法未研究,https://discuss.leetcode.com/topic/67590/java-o-n