#28_implement_strstr().py

'''
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(len(needle)==0):
            return 0
        if(len(haystack)==0 or len(needle)>len(haystack)):
            return -1
        for i in range(len(haystack)):
            if(haystack[i]==needle[0]):
                if(haystack[i:i+len(needle)]==needle):
                    return i
        return -1