ImplementStrStr.java

package string;

/**
 * Created by gouthamvidyapradhan on 24/06/2017.
 * Implement strStr().
 * <p>
 * Returns the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack.
 * <p>
 * Solution O(N ^ 2)
 */
public class ImplementStrStr {
    public static void main(String[] args) throws Exception {
        System.out.println(new ImplementStrStr().strStr("AABB", ""));
    }

    public int strStr(String haystack, String needle) {
        if (haystack.isEmpty() && needle.isEmpty()) return 0;
        if (needle.isEmpty()) return 0;
        for (int i = 0, l = haystack.length(); i < l; i++) {
            if (haystack.charAt(i) == needle.charAt(0)) {
                if (isEqual(haystack, needle, i))
                    return i;
            }
        }
        return -1;
    }

    private boolean isEqual(String haystack, String needle, int i) {
        int hL = haystack.length();
        int nL = needle.length();
        int j = 0;
        while (i < hL && j < nL) {
            if (haystack.charAt(i) != needle.charAt(j))
                return false;
            i++;
            j++;
        }
        return j >= nL;
    }


}