LeetCode - Find The Index Of The First Occurrence In A String

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今天我們要講解的是 [Find The Index Of The First Occurrence In A String]，這在 LeetCode 算是比較簡單的題目，讓我們一起開始吧！

進來之前請先注意，我的方式不一定完全正確，只是依照我自己的理念進行撰寫，所以如果程式上有什麼更好的解法，歡迎提出見解。

這次題目

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

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.

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.

自已解法

這個題目主要是針對haystack來檢查是第一個index才與needle相同，首先我們先建立len與output的值。

var strStr = function(haystack, needle) {
    let len = needle.length;
    let output = -1;

    return output;
};

接著我們針對haystack去跑迴圈，另外避免白跑，我們需要在i < (size - len + 1)之前直接結束，接著透過slice進行字串切割來進行比對，正確我們就可以直接跳脫並寫入output值。

var strStr = function(haystack, needle) {
    let len = needle.length;
    let output = -1;
    for(let i = 0; i < haystack.length - len + 1; i++) {
        if (haystack.slice(i, i + len) === needle) {
            output = i;
            break;
        }
    }
    return output;
};

實作結果

以上就是這次的實作，感謝各位！

Image From LeetCode