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


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, needle):
        :type haystack: str
        :type needle: str
        :rtype: int
        ln = len(needle)
        lh = len(haystack)
        if ln == 0:
            return 0
        if lh < ln:
            return -1

        i = 0

        while i <= lh - ln:
            if haystack[i] == needle[0] and haystack[i:i+ln] == needle:
                return i
            i += 1
        return -1