28.md

28. 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

my thoughts:

1. check the first char then check the substring.

my solution:

**********32ms
class Solution(object):
    def strStr(self, haystack, needle):
        """
        :type haystack: str
        :type needle: str
        :rtype: int
        """
        if not needle:
            return 0
        if not haystack:
            return -1
        i = 0
        lh = len(haystack)
        ln = len(needle)
        while i + ln <= lh:
            if haystack[i] != needle[0]:
                i += 1
                continue
            elif haystack[i:i+ln] == needle:
                return i
            i += 1
        return -1

my comments:

from other ppl's solution:

1. built-in func, find(), 25ms:
class Solution(object):
    def strStr(self, haystack, needle):
        """
        :type haystack: str
        :type needle: str
        :rtype: int
        """
        return haystack.find(needle)
		
2. substring in/not in string, 28ms:
class Solution(object):
    def strStr(self, haystack, needle):
        """
        :type haystack: str
        :type needle: str
        :rtype: int
        """
        if needle not in haystack:
            return -1
        return haystack.index(needle)