leetcode-problemset/leetcode-cn/problem (English)/判断子序列(English) [is-subsequence].html

<p>Given two strings <code>s</code> and <code>t</code>, return <code>true</code><em> if </em><code>s</code><em> is a <strong>subsequence</strong> of </em><code>t</code><em>, or </em><code>false</code><em> otherwise</em>.</p>

<p>A <strong>subsequence</strong> of a string is a new string that is formed from the original string by deleting some (can be none) of the characters without disturbing the relative positions of the remaining characters. (i.e., <code>&quot;ace&quot;</code> is a subsequence of <code>&quot;<u>a</u>b<u>c</u>d<u>e</u>&quot;</code> while <code>&quot;aec&quot;</code> is not).</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<pre><strong>Input:</strong> s = "abc", t = "ahbgdc"
<strong>Output:</strong> true
</pre><p><strong class="example">Example 2:</strong></p>
<pre><strong>Input:</strong> s = "axc", t = "ahbgdc"
<strong>Output:</strong> false
</pre>
<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>0 &lt;= s.length &lt;= 100</code></li>
	<li><code>0 &lt;= t.length &lt;= 10<sup>4</sup></code></li>
	<li><code>s</code> and <code>t</code> consist only of lowercase English letters.</li>
</ul>

<p>&nbsp;</p>
<strong>Follow up:</strong> Suppose there are lots of incoming <code>s</code>, say <code>s<sub>1</sub>, s<sub>2</sub>, ..., s<sub>k</sub></code> where <code>k &gt;= 10<sup>9</sup></code>, and you want to check one by one to see if <code>t</code> has its subsequence. In this scenario, how would you change your code?