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44 lines
1.5 KiB
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44 lines
1.5 KiB
HTML
<p>An integer <code>x</code> is a <strong>good</strong> if after rotating each digit individually by 180 degrees, we get a valid number that is different from <code>x</code>. Each digit must be rotated - we cannot choose to leave it alone.</p>
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<p>A number is valid if each digit remains a digit after rotation. For example:</p>
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<ul>
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<li><code>0</code>, <code>1</code>, and <code>8</code> rotate to themselves,</li>
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<li><code>2</code> and <code>5</code> rotate to each other (in this case they are rotated in a different direction, in other words, <code>2</code> or <code>5</code> gets mirrored),</li>
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<li><code>6</code> and <code>9</code> rotate to each other, and</li>
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<li>the rest of the numbers do not rotate to any other number and become invalid.</li>
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</ul>
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<p>Given an integer <code>n</code>, return <em>the number of <strong>good</strong> integers in the range </em><code>[1, n]</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 = 10
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<strong>Output:</strong> 4
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<strong>Explanation:</strong> There are four good numbers in the range [1, 10] : 2, 5, 6, 9.
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Note that 1 and 10 are not good numbers, since they remain unchanged after rotating.
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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> 0
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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
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<strong>Output:</strong> 1
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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>4</sup></code></li>
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</ul>
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