Problem URL: Find the index of the first occurrence in a string

We will create a substring of length of the needle and compare it with the needle, if we find a match, we return the index as result, otherwise return -1.

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(n)
Space Complexity: O(1)

We can use python's builtin functions to achieve it even easier.

class Solution:
    def strStr(self, haystack: str, needle: str) -> int:
        if needle not in haystack:
            return -1
        return haystack.index(needle)

Time Complexity: O(n)
Space Complexity: O(1)