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41 lines
1.5 KiB
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41 lines
1.5 KiB
HTML
<p>Given a string <code>s</code> consisting of lowercase English letters, return <em>the first letter to appear <strong>twice</strong></em>.</p>
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<p><strong>Note</strong>:</p>
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<ul>
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<li>A letter <code>a</code> appears twice before another letter <code>b</code> if the <strong>second</strong> occurrence of <code>a</code> is before the <strong>second</strong> occurrence of <code>b</code>.</li>
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<li><code>s</code> will contain at least one letter that appears twice.</li>
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</ul>
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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 = "abccbaacz"
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<strong>Output:</strong> "c"
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<strong>Explanation:</strong>
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The letter 'a' appears on the indexes 0, 5 and 6.
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The letter 'b' appears on the indexes 1 and 4.
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The letter 'c' appears on the indexes 2, 3 and 7.
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The letter 'z' appears on the index 8.
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The letter 'c' is the first letter to appear twice, because out of all the letters the index of its second occurrence is the smallest.
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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 = "abcdd"
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<strong>Output:</strong> "d"
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<strong>Explanation:</strong>
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The only letter that appears twice is 'd' so we return 'd'.
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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>2 <= s.length <= 100</code></li>
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<li><code>s</code> consists of lowercase English letters.</li>
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<li><code>s</code> has at least one repeated letter.</li>
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</ul>
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