LeetCode 028 Implement strStr()

题目要求：Implement strStr()

Implement strStr().

Returns the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack.

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;

    }