freeCodeCamp/curriculum/challenges/chinese/08-coding-interview-prep/project-euler/problem-15-lattice-paths.ch...

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---
id: 5900f37b1000cf542c50fe8e
challengeType: 5
title: 'Problem 15: Lattice paths'
videoUrl: ''
localeTitle: 问题15格子路径
---
## Description
<section id="description">从2×2网格的左上角开始只能向右和向下移动右下角有6条路线。 <img class="img-responsive center-block" alt="6 2乘2网格的图表显示了右下角的所有路线" src="https://i.imgur.com/1Atixoj.gif"><p>通过给定的<code>gridSize</code>有多少这样的路由? </p></section>
## Instructions
<section id="instructions">
</section>
## Tests
<section id='tests'>
```yml
tests:
- text: <code>latticePaths(4)</code>应该返回70。
testString: 'assert.strictEqual(latticePaths(4), 70, "<code>latticePaths(4)</code> should return 70.");'
- text: <code>latticePaths(9)</code>应该返回48620。
testString: 'assert.strictEqual(latticePaths(9), 48620, "<code>latticePaths(9)</code> should return 48620.");'
- text: <code>latticePaths(20)</code>应该返回137846528820。
testString: 'assert.strictEqual(latticePaths(20), 137846528820, "<code>latticePaths(20)</code> should return 137846528820.");'
```
</section>
## Challenge Seed
<section id='challengeSeed'>
<div id='js-seed'>
```js
function latticePaths(gridSize) {
// Good luck!
return true;
}
latticePaths(4);
```
</div>
</section>
## Solution
<section id='solution'>
```js
// solution required
```
</section>