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40 lines
1.5 KiB
HTML
40 lines
1.5 KiB
HTML
<p>Your music player contains <code>n</code> different songs. You want to listen to <code>goal</code> songs (not necessarily different) during your trip. To avoid boredom, you will create a playlist so that:</p>
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<ul>
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<li>Every song is played <strong>at least once</strong>.</li>
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<li>A song can only be played again only if <code>k</code> other songs have been played.</li>
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</ul>
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<p>Given <code>n</code>, <code>goal</code>, and <code>k</code>, return <em>the number of possible playlists that you can create</em>. Since the answer can be very large, return it <strong>modulo</strong> <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 = 3, goal = 3, k = 1
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<strong>Output:</strong> 6
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<strong>Explanation:</strong> There are 6 possible playlists: [1, 2, 3], [1, 3, 2], [2, 1, 3], [2, 3, 1], [3, 1, 2], and [3, 2, 1].
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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 = 2, goal = 3, k = 0
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<strong>Output:</strong> 6
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<strong>Explanation:</strong> There are 6 possible playlists: [1, 1, 2], [1, 2, 1], [2, 1, 1], [2, 2, 1], [2, 1, 2], and [1, 2, 2].
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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 = 2, goal = 3, k = 1
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<strong>Output:</strong> 2
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<strong>Explanation:</strong> There are 2 possible playlists: [1, 2, 1] and [2, 1, 2].
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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>0 <= k < n <= goal <= 100</code></li>
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</ul>
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