human
Solve in Python:
Implement strStr().

Return the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack.

Example 1:

Input: haystack = "hello", needle = "ll"
Output: 2

Example 2:

Input: haystack = "aaaaa", needle = "bba"
Output: -1

Clarification:

What should we return when needle is an empty string? This is a great question to ask during an interview.

For the purpose of this problem, we will return 0 when needle is an empty string. This is consistent to C's strstr() and Java's indexOf().

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Here should we return when needle is an empty string?
assistant
#Here should we return when needle is an empty string.

class Solution:
     def strStr(self, haystack, needle):
         """
         :type haystack: str
         :type needle: str
         :rtype: int
         """
         if not needle:
             return 0
         
         for i in range(0, len(haystack)-len(needle)+1):
             match = True
             for j in range(len(needle)):
                 if haystack[i+j] != needle[j]:
                     match = False
                     break
             if match:
                 return i
         
         return -1