28. Implement strStr().py

class Solution:
    def strStr(self, haystack: str, needle: str) -> int:
        # Return 0 if needle is an empty string
        if not needle:
            return 0
        
        # Return -1 if length of needle is longer than haystack (not possible to match)
        if len(needle) > len(haystack):
            return -1
        
        # Loop through haystack minus length of needle (otherwise can't match all char)
        # Do a string comparison at each index
        for i in range(len(haystack) - len(needle) + 1):
            if haystack[i:i + len(needle)] == needle:
                return i
        
        return -1