46 lines
801 B
Markdown
46 lines
801 B
Markdown
---
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id: 597b2b2a2702b44414742771
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title: 阶乘
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challengeType: 5
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videoUrl: ''
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---
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# --description--
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<p>编写一个函数来返回一个数字的阶乘。 </p><p>一个数字的因子由下式给出： </p> N！ = n \*（n-1）\*（n-2）\* ..... \* 1 <p>例如：3！ = 3 * 2 * 1 = 6 4！ = 4 * 3 * 2 * 1 = 24 </p><p>注意：0！ = 1 </p>
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# --hints--
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`factorial`是一种功能。
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```js
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assert(typeof factorial === 'function');
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```
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`factorial(2)`应该返回一个数字。
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```js
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assert(typeof factorial(2) === 'number');
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```
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`factorial(3)`应该返回6.“）
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```js
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assert.equal(factorial(3), 6);
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```
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`factorial(3)`应返回120.“）
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```js
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assert.equal(factorial(5), 120);
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```
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`factorial(3)`应返回3,628,800。“）
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```js
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assert.equal(factorial(10), 3628800);
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```
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# --solutions--
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