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49 lines
1.8 KiB
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49 lines
1.8 KiB
HTML
<p>An attendance record for a student can be represented as a string where each character signifies whether the student was absent, late, or present on that day. The record only contains the following three characters:</p>
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<ul>
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<li><code>'A'</code>: Absent.</li>
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<li><code>'L'</code>: Late.</li>
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<li><code>'P'</code>: Present.</li>
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</ul>
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<p>Any student is eligible for an attendance award if they meet <strong>both</strong> of the following criteria:</p>
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<ul>
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<li>The student was absent (<code>'A'</code>) for <strong>strictly</strong> fewer than 2 days <strong>total</strong>.</li>
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<li>The student was <strong>never</strong> late (<code>'L'</code>) for 3 or more <strong>consecutive</strong> days.</li>
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</ul>
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<p>Given an integer <code>n</code>, return <em>the <strong>number</strong> of possible attendance records of length</em> <code>n</code><em> that make a student eligible for an attendance award. The answer may be very large, so return it <strong>modulo</strong> </em><code>10<sup>9</sup> + 7</code>.</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> n = 2
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<strong>Output:</strong> 8
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<strong>Explanation:</strong> There are 8 records with length 2 that are eligible for an award:
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"PP", "AP", "PA", "LP", "PL", "AL", "LA", "LL"
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Only "AA" is not eligible because there are 2 absences (there need to be fewer than 2).
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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> n = 1
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<strong>Output:</strong> 3
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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> n = 10101
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<strong>Output:</strong> 183236316
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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 <= n <= 10<sup>5</sup></code></li>
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</ul>
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