update

leetcode/problem/greatest-english-letter-in-upper-and-lower-case.html

@@ -0,0 +1,40 @@
+<p>Given a string of English letters <code>s</code>, return <em>the <strong>greatest </strong>English letter which occurs as <strong>both</strong> a lowercase and uppercase letter in</em> <code>s</code>. The returned letter should be in <strong>uppercase</strong>. If no such letter exists, return <em>an empty string</em>.</p>
+
+<p>An English letter <code>b</code> is <strong>greater</strong> than another letter <code>a</code> if <code>b</code> appears <strong>after</strong> <code>a</code> in the English alphabet.</p>
+
+<p>&nbsp;</p>
+<p><strong>Example 1:</strong></p>
+
+<pre>
+<strong>Input:</strong> s = &quot;l<strong><u>Ee</u></strong>TcOd<u><strong>E</strong></u>&quot;
+<strong>Output:</strong> &quot;E&quot;
+<strong>Explanation:</strong>
+The letter &#39;E&#39; is the only letter to appear in both lower and upper case.
+</pre>
+
+<p><strong>Example 2:</strong></p>
+
+<pre>
+<strong>Input:</strong> s = &quot;a<strong><u>rR</u></strong>AzFif&quot;
+<strong>Output:</strong> &quot;R&quot;
+<strong>Explanation:</strong>
+The letter &#39;R&#39; is the greatest letter to appear in both lower and upper case.
+Note that &#39;A&#39; and &#39;F&#39; also appear in both lower and upper case, but &#39;R&#39; is greater than &#39;F&#39; or &#39;A&#39;.
+</pre>
+
+<p><strong>Example 3:</strong></p>
+
+<pre>
+<strong>Input:</strong> s = &quot;AbCdEfGhIjK&quot;
+<strong>Output:</strong> &quot;&quot;
+<strong>Explanation:</strong>
+There is no letter that appears in both lower and upper case.
+</pre>
+
+<p>&nbsp;</p>
+<p><strong>Constraints:</strong></p>
+
+<ul>
+	<li><code>1 &lt;= s.length &lt;= 1000</code></li>
+	<li><code>s</code> consists of lowercase and uppercase English letters.</li>
+</ul>