28. Implement strStr()

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