56 lines
1.3 KiB
Markdown
56 lines
1.3 KiB
Markdown
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---
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id: 5900f5091000cf542c51001b
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challengeType: 5
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title: 'Problem 408: Admissible paths through a grid'
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videoUrl: ''
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localeTitle: 问题408：通过网格的可允许路径
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---
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## Description
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<section id="description">如果x，y和x + y都是正的正方形，那么我们称格子点（x，y）是不允许的。例如，（9,16）是不允许的，而（0,4），（3,1）和（9,4）则不允许。 <p>考虑从点（x1，y1）到点（x2，y2）的路径，仅使用北或东的单位步长。如果其中间点都不允许，我们可以称这样的路径是可以接受的。 </p><p>令P（n）是从（0,0）到（n，n）的可允许路径的数量。可以证实P（5）= 252，P（16）= 596994440和P（1000）mod 1 000 000 007 = 341920854。 </p><p>求P（10 000 000）mod 1 000 000 007。 </p></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>euler408()</code>应该返回299742733。
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testString: 'assert.strictEqual(euler408(), 299742733, "<code>euler408()</code> should return 299742733.");'
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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 euler408() {
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// Good luck!
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return true;
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}
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euler408();
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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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