Given two strings needle and haystack, return the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack.

Example 1:

Input: haystack = "sadbutsad", needle = "sad"
Output: 0
Explanation: "sad" occurs at index 0 and 6.
The first occurrence is at index 0, so we return 0.
Example 2:

Input: haystack = "leetcode", needle = "leeto"
Output: -1
Explanation: "leeto" did not occur in "leetcode", so we return -1.

Constraints:

1 <= haystack.length, needle.length <= 104
haystack and needle consist of only lowercase English characters.

# @param {String} haystack
# @param {String} needle
# @return {Integer}
def str_str(haystack, needle)
    h_size = haystack.size
    n_size = needle.size
    return -1 if h_size < n_size
    
    i = 0
    while i <= h_size
        return i if haystack[i, n_size] == needle 
        i += 1
    end
    return -1
end