<p>A sentence consists of lowercase letters (<code>'a'</code> to <code>'z'</code>), digits (<code>'0'</code> to <code>'9'</code>), hyphens (<code>'-'</code>), punctuation marks (<code>'!'</code>, <code>'.'</code>, and <code>','</code>), and spaces (<code>''</code>) only. Each sentence can be broken down into <strong>one or more tokens</strong> separated by one or more spaces <code>''</code>.</p>
<p>A token is a valid word if <strong>all three</strong> of the following are true:</p>
<ul>
<li>It only contains lowercase letters, hyphens, and/or punctuation (<strong>no</strong> digits).</li>
<li>There is <strong>at most one</strong> hyphen <code>'-'</code>. If present, it <strong>must</strong> be surrounded by lowercase characters (<code>"a-b"</code> is valid, but <code>"-ab"</code> and <code>"ab-"</code> are not valid).</li>
<li>There is <strong>at most one</strong> punctuation mark. If present, it <strong>must</strong> be at the <strong>end</strong> of the token (<code>"ab,"</code>, <code>"cd!"</code>, and <code>"."</code> are valid, but <code>"a!b"</code> and <code>"c.,"</code> are not valid).</li>
</ul>
<p>Examples of valid words include <code>"a-b."</code>, <code>"afad"</code>, <code>"ba-c"</code>, <code>"a!"</code>, and <code>"!"</code>.</p>
<p>Given a string <code>sentence</code>, return <em>the <strong>number</strong> of valid words in </em><code>sentence</code>.</p>
<strong>Explanation:</strong> The valid words in the sentence are "alice", "and", "bob", "are", and "playing".
"stone-game10" is invalid because it contains digits.
<li><code>sentence</code> only contains lowercase English letters, digits, <code>''</code>, <code>'-'</code>, <code>'!'</code>, <code>'.'</code>, and <code>','</code>.</li>
<li>There will be at least <code>1</code> token.</li>
