'''
Problem 57

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.


'''
class Solution:
    def strStr(self, haystack: str, needle: str) -> int:
        if needle == "":
            return 0
        for i in range(len(haystack) + 1 - len(needle)):
            if haystack[i : i + len(needle)] == needle:
                return i
        return -1