28. Find the Index of the First Occurrence in a String

Medium (Trung bình) Python 🔗 Xem trên LeetCode

📋 Đề Bài

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.

💻 Lời Giải

Python 0028-find-the-index-of-the-first-occurrence-in-a-string.py 
class Solution:
    def strStr(self, haystack: str, needle: str) -> int:
        n = len(haystack)
        k = len(needle)
        
        for i in range(n - k + 1):
            if haystack[i:k + i] == needle:
                return i
            
        return -1