FindtheIndexoftheFirstOccurrenceinaString.py

"""
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 <= 104
haystack and needle consist of only lowercase English characters.
"""


class Solution:
    def strStr(self, haystack: str, needle: str) -> int:
        if not needle:
            return 0
        if len(needle) > len(haystack):
            return -1

        for i in range(len(haystack) - len(needle) + 1):
            if haystack[i:i + len(needle)] == needle:
                return i

        return -1


# Example usage
if __name__ == "__main__":
    solution = Solution()
    haystack1, needle1 = "sadbutsad", "sad"
    haystack2, needle2 = "leetcode", "leeto"
    print(solution.strStr(haystack1, needle1))  # Expected output: 0
    print(solution.strStr(haystack2, needle2))  # Expected output: -1