0028 Implement strStr()

public class Solution {
    public int StrStr(string haystack, string needle) {
        if (needle != "")
        {
            if (haystack == "")
                return -1;

            var nl = needle.Length;
            for (var i = 0; i < haystack.Length; i++)
            {
                if (haystack[i] == needle[0])
                {
                    if (nl != 1)
                    {
                        bool find = true;
                        for (var j = 1; j < nl; j++)
                        {
                            if (i + j >= haystack.Length || haystack[i + j] != needle[j])
                            {
                                find = false;
                                break;
                            }
                        }

                        if (find)
                            return i;
                    }
                    else
                    {
                        return i;
                    }
                }
            }

            return -1;
        }

        return 0;


    }
}