Day8- [再不學python我要被世界淘汰了] Leetcode 28_V2

Leetcode 第28題，這次用slicing string 去做做看

28. 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.

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.

我的作法:

思路 :

1. 定義m為haystack長度，n為needle長度
2. 若needle 不在haystack中，輸出-1
3. 專注看haystack
4. 利用for迴圈從haystack一開始往後找needle長度的字串 ，即找haystack[i:i+n]
5. 若haystack[i:i+n] = needle，則回傳haystack的字首開頭位置號碼