LeetCode – Implementar strStr () (Java)

public int strStr(String haystack, String needle) {
    if(haystack==null || needle==null)    
        return 0;
 
    if(needle.length() == 0)
        return 0;
 
    for(int i=0; i<haystack.length(); i++){
        if(i + needle.length() > haystack.length())
            return -1;
 
        int m = i;
        for(int j=0; j<needle.length(); j++){
            if(needle.charAt(j)==haystack.charAt(m)){
                if(j==needle.length()-1)
                    return i;
                m++;
            }else{
                break;
            }
 
        }    
    }   
 
    return -1;
}

public int strStr(String haystack, String needle) {
        if(haystack==null || needle==null)    
            return 0;
 
	int h = haystack.length();
	int n = needle.length();
 
	if (n > h)
		return -1;
	if (n == 0)
		return 0;
 
	int[] next = getNext(needle);
	int i = 0;
 
	while (i <= h - n) {
		int success = 1;
		for (int j = 0; j < n; j++) {
			if (needle.charAt(0) != haystack.charAt(i)) {
				success = 0;
				i++;
				break;
			} else if (needle.charAt(j) != haystack.charAt(i + j)) {
				success = 0;
				i = i + j - next[j - 1];
				break;
			}
		}
		if (success == 1)
			return i;
	}
 
	return -1;
}
 
//calculate KMP array
public int[] getNext(String needle) {
	int[] next = new int[needle.length()];
	next[0] = 0;
 
	for (int i = 1; i < needle.length(); i++) {
		int index = next[i - 1];
		while (index > 0 && needle.charAt(index) != needle.charAt(i)) {
			index = next[index - 1];
		}
 
		if (needle.charAt(index) == needle.charAt(i)) {
			next[i] = next[i - 1] + 1;
		} else {
			next[i] = 0;
		}
	}
 
	return next;
}