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41 lines
1.6 KiB
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<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>
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<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>
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<p> </p>
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<p><strong>Example 1:</strong></p>
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<pre>
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<strong>Input:</strong> s = "l<strong><u>Ee</u></strong>TcOd<u><strong>E</strong></u>"
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<strong>Output:</strong> "E"
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<strong>Explanation:</strong>
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The letter 'E' is the only letter to appear in both lower and upper case.
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</pre>
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<p><strong>Example 2:</strong></p>
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<pre>
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<strong>Input:</strong> s = "a<strong><u>rR</u></strong>AzFif"
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<strong>Output:</strong> "R"
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<strong>Explanation:</strong>
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The letter 'R' is the greatest letter to appear in both lower and upper case.
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Note that 'A' and 'F' also appear in both lower and upper case, but 'R' is greater than 'F' or 'A'.
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</pre>
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<p><strong>Example 3:</strong></p>
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<pre>
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<strong>Input:</strong> s = "AbCdEfGhIjK"
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<strong>Output:</strong> ""
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<strong>Explanation:</strong>
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There is no letter that appears in both lower and upper case.
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</pre>
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<p> </p>
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<p><strong>Constraints:</strong></p>
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<ul>
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<li><code>1 <= s.length <= 1000</code></li>
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<li><code>s</code> consists of lowercase and uppercase English letters.</li>
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</ul>
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