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Description
tab: English
<p>Given two strings <code>needle</code> and <code>haystack</code>, return the index of the first occurrence of <code>needle</code> in <code>haystack</code>, or <code>-1</code> if <code>needle</code> is not part of <code>haystack</code>.</p>
<p> </p>
<p><strong class="example">Example 1:</strong></p>
<pre>
<strong>Input:</strong> haystack = "sadbutsad", needle = "sad"
<strong>Output:</strong> 0
<strong>Explanation:</strong> "sad" occurs at index 0 and 6.
The first occurrence is at index 0, so we return 0.
</pre>
<p><strong class="example">Example 2:</strong></p>
<pre>
<strong>Input:</strong> haystack = "leetcode", needle = "leeto"
<strong>Output:</strong> -1
<strong>Explanation:</strong> "leeto" did not occur in "leetcode", so we return -1.
</pre>
<p> </p>
<p><strong>Constraints:</strong></p>
<ul>
<li><code>1 <= haystack.length, needle.length <= 10<sup>4</sup></code></li>
<li><code>haystack</code> and <code>needle</code> consist of only lowercase English characters.</li>
</ul>
---
[submissions](https://leetcode.com/problems/find-the-index-of-the-first-occurrence-in-a-string/submissions/) | [solutions](https://leetcode.com/problems/find-the-index-of-the-first-occurrence-in-a-string/solutions/)
tab: 中文
<p>给你两个字符串 <code>haystack</code> 和 <code>needle</code> ，请你在 <code>haystack</code> 字符串中找出 <code>needle</code> 字符串的第一个匹配项的下标（下标从 0 开始）。如果 <code>needle</code> 不是 <code>haystack</code> 的一部分，则返回 <code>-1</code><strong> </strong>。</p>
<p> </p>
<p><strong class="example">示例 1：</strong></p>
<pre>
<strong>输入：</strong>haystack = "sadbutsad", needle = "sad"
<strong>输出：</strong>0
<strong>解释：</strong>"sad" 在下标 0 和 6 处匹配。
第一个匹配项的下标是 0 ，所以返回 0 。
</pre>
<p><strong class="example">示例 2：</strong></p>
<pre>
<strong>输入：</strong>haystack = "leetcode", needle = "leeto"
<strong>输出：</strong>-1
<strong>解释：</strong>"leeto" 没有在 "leetcode" 中出现，所以返回 -1 。
</pre>
<p> </p>
<p><strong>提示：</strong></p>
<ul>
<li><code>1 <= haystack.length, needle.length <= 10<sup>4</sup></code></li>
<li><code>haystack</code> 和 <code>needle</code> 仅由小写英文字符组成</li>
</ul>
---
[提交记录](https://leetcode.cn/problems/find-the-index-of-the-first-occurrence-in-a-string/submissions/) | [题解](https://leetcode.cn/problems/find-the-index-of-the-first-occurrence-in-a-string/solution/)
Solutions & Notes
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