leetcode-problemset/leetcode/problem/valid-number.html

<p>A <strong>valid number</strong> can be split up into these components (in order):</p>

<ol>
	<li>A <strong>decimal number</strong> or an <strong>integer</strong>.</li>
	<li>(Optional) An <code>&#39;e&#39;</code> or <code>&#39;E&#39;</code>, followed by an <strong>integer</strong>.</li>
</ol>

<p>A <strong>decimal number</strong> can be split up into these components (in order):</p>

<ol>
	<li>(Optional) A sign character (either <code>&#39;+&#39;</code> or <code>&#39;-&#39;</code>).</li>
	<li>One of the following formats:
	<ol>
		<li>One or more digits, followed by a dot <code>&#39;.&#39;</code>.</li>
		<li>One or more digits, followed by a dot <code>&#39;.&#39;</code>, followed by one or more digits.</li>
		<li>A dot <code>&#39;.&#39;</code>, followed by one or more digits.</li>
	</ol>
	</li>
</ol>

<p>An <strong>integer</strong> can be split up into these components (in order):</p>

<ol>
	<li>(Optional) A sign character (either <code>&#39;+&#39;</code> or <code>&#39;-&#39;</code>).</li>
	<li>One or more digits.</li>
</ol>

<p>For example, all the following are valid numbers: <code>[&quot;2&quot;, &quot;0089&quot;, &quot;-0.1&quot;, &quot;+3.14&quot;, &quot;4.&quot;, &quot;-.9&quot;, &quot;2e10&quot;, &quot;-90E3&quot;, &quot;3e+7&quot;, &quot;+6e-1&quot;, &quot;53.5e93&quot;, &quot;-123.456e789&quot;]</code>, while the following are not valid numbers: <code>[&quot;abc&quot;, &quot;1a&quot;, &quot;1e&quot;, &quot;e3&quot;, &quot;99e2.5&quot;, &quot;--6&quot;, &quot;-+3&quot;, &quot;95a54e53&quot;]</code>.</p>

<p>Given a string <code>s</code>, return <code>true</code><em> if </em><code>s</code><em> is a <strong>valid number</strong></em>.</p>

<p>&nbsp;</p>
<p><strong>Example 1:</strong></p>

<pre>
<strong>Input:</strong> s = &quot;0&quot;
<strong>Output:</strong> true
</pre>

<p><strong>Example 2:</strong></p>

<pre>
<strong>Input:</strong> s = &quot;e&quot;
<strong>Output:</strong> false
</pre>

<p><strong>Example 3:</strong></p>

<pre>
<strong>Input:</strong> s = &quot;.&quot;
<strong>Output:</strong> false
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= s.length &lt;= 20</code></li>
	<li><code>s</code> consists of only English letters (both uppercase and lowercase), digits (<code>0-9</code>), plus <code>&#39;+&#39;</code>, minus <code>&#39;-&#39;</code>, or dot <code>&#39;.&#39;</code>.</li>
</ul>