Implement strStr().

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

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

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

class Solution:
    def strStr(self, haystack, needle):
        """
        :type haystack: str
        :type needle: str
        :rtype: int
        """
        if not needle:
            return 0
        index = 0
        n = len(needle)
        i = 0
        while i < len(haystack):
            if haystack[i] == needle[index]:
                index += 1
                i += 1
                if index == n:
                    return i - n 
            else:
                i = i - index + 1
                index = 0
        return -1

class Solution:
    def strStr(self, haystack, needle):
        """
        :type haystack: str
        :type needle: str
        :rtype: int
        """
        return haystack.find(needle)