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;

}