📌Problem

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 <= $5 * 10^4$
• haystack and needle consist of only lower-case English characters.

leetcode 에서 풀기

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📝Solution

class Solution:
    def strStr(self, haystack: str, needle: str) -> int:
        
        for i in range(len(haystack)-len(needle)+1):
            if haystack[i:i+len(needle)]==needle:
                return i
        
        return -1

• Time complexity : $O(NM), N=|haystack|\ , M=|needle|$