## DEV Community

Abhishek Chaudhary

Posted on

# Implement strStr()

Implement strStr().

Given two strings `needle` and `haystack`, 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

Constraints:

• `1 <= haystack.length, needle.length <= 104`
• `haystack` and `needle` consist of only lowercase English characters.

SOLUTION:

``````class Solution:
def strStr(self, haystack: str, needle: str) -> int:
n = len(haystack)
k = len(needle)
exists = {needle}
for i in range(0, n - k + 1):
if haystack[i : i + k] in exists:
return i
return -1
``````