Find the Index of the First Occurrence in a String

Problem Statement

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.

Examples

Example 1:

Input: haystack = "sadbutsad", needle = "sad"
Output: 0
Explanation: "sad" occurs at index 0 and 6.
The first occurrence is at index 0, so we return 0.

Example 2:

Input: haystack = "leetcode", needle = "leeto"
Output: -1
Explanation: "leeto" did not occur in "leetcode", so we return -1.

Constraints

• 1 <= haystack.length, needle.length <= 10^4
• haystack and needle consist of only lowercase English characters.

Code Template

class Solution:
    def strStr(self, haystack: str, needle: str) -> int:
        # Your code here
        pass

Solutions

• Solution 1: This approach checks every possible starting position in haystack and compares the substring with needle. It has a time complexity of O(n * m) and a space complexity of O(1).

Back to Problem List

Back to Categories