66 lines
1.3 KiB
Markdown
66 lines
1.3 KiB
Markdown
---
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id: 5900f4371000cf542c50ff49
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challengeType: 5
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title: 'Problem 202: Laserbeam'
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---
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## Description
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<section id='description'>
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Three mirrors are arranged in the shape of an equilateral triangle, with their reflective surfaces pointing inwards. There is an infinitesimal gap at each vertex of the triangle through which a laser beam may pass.
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Label the vertices A, B and C. There are 2 ways in which a laser beam may enter vertex C, bounce off 11 surfaces, then exit through the same vertex: one way is shown below; the other is the reverse of that.
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There are 80840 ways in which a laser beam may enter vertex C, bounce off 1000001 surfaces, then exit through the same vertex.
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In how many ways can a laser beam enter at vertex C, bounce off 12017639147 surfaces, then exit through the same vertex?
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</section>
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## Instructions
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<section id='instructions'>
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</section>
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## Tests
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<section id='tests'>
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```yml
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tests:
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- text: <code>euler202()</code> should return 1209002624.
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testString: assert.strictEqual(euler202(), 1209002624, '<code>euler202()</code> should return 1209002624.');
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```
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</section>
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## Challenge Seed
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<section id='challengeSeed'>
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<div id='js-seed'>
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```js
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function euler202() {
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// Good luck!
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return true;
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}
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euler202();
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```
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</div>
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</section>
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## Solution
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<section id='solution'>
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```js
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// solution required
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```
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</section>
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