LeetCode Top Interview 150

28. Implement strStr()

Easy

Implement strStr().

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

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().

Example 1:

Input: haystack = “hello”, needle = “ll”

Output: 2

Example 2:

Input: haystack = “aaaaa”, needle = “bba”

Output: -1

Example 3:

Input: haystack = “”, needle = “”

Output: 0

Constraints:

• 0 <= haystack.length, needle.length <= 5 * 104
• haystack and needle consist of only lower-case English characters.

Solution

class Solution:
    def strStr(self, haystack: str, needle: str) -> int:
        if not needle:
            return 0
        m = len(haystack)
        n = len(needle)
        for start in range(m - n + 1):
            if haystack[start:start + n] == needle:
                return start
        return -1

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