28. Find the Index of the First Occurrence in a String

https://leetcode.com/problems/find-the-index-of-the-first-occurrence-in-a-string

Python

class Solution:
    def strStr(self, haystack: str, needle: str) -> int:
        n, m = len(haystack), len(needle)
        if n < m:
            return -1
        if n == m:
            return 0 if haystack == needle else -1

        for i in range(n-m+1):
            if ''.join([haystack[i:i+m]]) == needle:
                return i
        return -1