[LC] 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

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().

 

Time: O(M * N)

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
        len_haystack, len_needle = len(haystack), len(needle)
        for i in range(0, len_haystack - len_needle + 1):
            cur = haystack[i]
            if cur == needle[0]:
                j = 0
                while j < len_needle:
                    if haystack[i + j] != needle[j]:
                        break
                    j += 1
                if j == len_needle:
                    return i
        return -1