FindTheIndexOfTheFirstOccurrenceInAString

Problem

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

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.

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:sup:`4`

• haystack and needle consist of only lowercase English characters.

Solution

Iterate through each character in haystack and check if the substring haystack[i:i + len(needle)] is equal to needle.

Pattern

Two Pointers, String, String Matching

Code

def strStr(haystack: str, needle: str) -> int:
    """Find the first occurrence of ``needle`` in ``haystack``.
    """
    for i, char in enumerate(haystack):
        if haystack[i:i + len(needle)] == needle:
            return i
    return -1

Test

>>> from FindTheIndexOfTheFirstOccurrenceInAString import strStr
>>> strStr('hello', 'll')
2
>>> strStr('aaaaa', 'bba')
-1

FindTheIndexOfTheFirstOccurrenceInAString.strStr(haystack: str, needle: str) → int

Find the first occurrence of needle in haystack.