java 459.重复子串模式（KMP）.java

Posted 2021-05-08

public class Solution {
   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;
}
}

public class Solution {
    private int[] getPrefix(String pattern) {
        int len = pattern.length();
        int[] lps = new int[len];
        lps[0] = 0;
        int matched = 0;
        for (int i = 1; i < len; i++) {
            while (matched > 0 && pattern.charAt(i) != pattern.charAt(matched)) {
                matched = lps[matched - 1];
            }
            if (pattern.charAt(i) == pattern.charAt(matched)) {
                matched++;
            }
            lps[i] = matched;
        }
        return lps;
    }
    public boolean repeatedSubstringPattern(String s) {
        int[] prefixFunction = getPrefix(s);
        int len = s.length();
        int last = prefixFunction[len - 1];
        return last != 0 && (len % (len - last) == 0);
    }
}