28. Implement strStr()

🟩 Easy

Question

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().

Complexity

• Time complexity: O(n)

• Space complexity: O(1)

Code

def strStr(self, haystack: str, needle: str) -> int:
    lenHaystack = len(haystack)
    lenNeedle = len(needle)
    if lenHaystack < lenNeedle:
        return -1
    elif lenNeedle == 0:
        return 0
    for i in range(lenHaystack):
        if haystack[i:i+lenNeedle] == needle:
            return i
    return -1