28_Implement_strStr.py

"""
https://leetcode.com/problems/implement-strstr/

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