_28.java

package com.fishercoder.solutions;
/**Implement strStr().

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

 */
public class _28 {
/**You could use substring as follows, or use two pointers to go through the haystack, if substring API call is not allowed.*/
public static int strStr(String haystack, String needle) {
    if (haystack == null || needle == null || haystack.length() < needle.length()) {
        return -1;
    }

    for (int i = 0; i <= haystack.length() - needle.length(); i++) {
        if (haystack.substring(i, i + needle.length()).equals(needle)) {
            return i;
        }
    }
    return -1;
}

    public static void main(String... args) {
//        String haystack = "a";
//        String needle = "";

//        String haystack = "mississippi";
//        String needle = "a";

        String haystack = "a";
        String needle = "a";
        strStr(haystack, needle);
    }
}