Implement strStr()

Implement strStr().

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

/*
Traverse all the possible starting points of haystack (from 0 to haystack.length() - needle.length()) and see if the following characters in haystack match those in needle.

time:O(m*n), space:O(1)
bonus: KMP, time:O(n),space:O(1)
*/

public class Solution {
    public int strStr(String haystack, String needle) {
        if (haystack == null || needle == null) {
            return -1;
        }
        int h = haystack.length();
        int n = needle.length();
        for (int i = 0; i < h - n + 1; i++) {
            int j = 0;
            for (j = 0; j < n; j++) {
                if (haystack.charAt(i + j) != needle.charAt(j)) {
                    break;
                }
            }
            if (j == n) {
                return i;
            }
        }
        return -1;
    }
}