<p>A <strong>wonderful</strong> string is a string where <strong>at most one</strong> letter appears an <strong>odd</strong> number of times.</p>
<ul>
<li>For example, <code>"ccjjc"</code> and <code>"abab"</code> are wonderful, but <code>"ab"</code> is not.</li>
</ul>
<p>Given a string <code>word</code> that consists of the first ten lowercase English letters (<code>'a'</code> through <code>'j'</code>), return <em>the <strong>number of wonderful non-empty substrings</strong> in </em><code>word</code><em>. If the same substring appears multiple times in </em><code>word</code><em>, then count <strong>each occurrence</strong> separately.</em></p>
<p>A <strong>substring</strong> is a contiguous sequence of characters in a string.</p>
<p> </p>
<p><strong>Example 1:</strong></p>
<pre>
<strong>Input:</strong> word = "aba"
<strong>Output:</strong> 4
<strong>Explanation:</strong> The four wonderful substrings are underlined below:
