---
title: Entropy
id: 599d15309e88c813a40baf58
challengeType: 5
videoUrl: ''
localeTitle: 熵
---

## Description
<section id="description">任务： <p>计算给定输入字符串的香农熵H. </p><p>给定谨慎的随机变量$ X $，它是$ N $“符号”（总字符）的字符串，由$ n $个不同的字符组成（对于二进制，n = 2），位/符号中X的香农熵是： </p><p> $ H_2（X）=  -  \ sum_ {i = 1} ^ n \ frac {count_i} {N} \ log_2 \ left（\ frac {count_i} {N} \ right）$ </p><p>其中$ count_i $是字符$ n_i $的计数。 </p></section>

## Instructions
<section id="instructions">
</section>

## Tests
<section id='tests'>

```yml
tests:
  - text: <code>entropy</code>是一种功能。
    testString: 'assert(typeof entropy === "function", "<code>entropy</code> is a function.");'
  - text: <code>entropy(&quot;0&quot;)</code>应该返回<code>0</code>
    testString: 'assert.equal(entropy("0"), 0, "<code>entropy("0")</code> should return <code>0</code>");'
  - text: <code>entropy(&quot;01&quot;)</code>应该返回<code>1</code>
    testString: 'assert.equal(entropy("01"), 1, "<code>entropy("01")</code> should return <code>1</code>");'
  - text: <code>entropy(&quot;0123&quot;)</code>应该返回<code>2</code>
    testString: 'assert.equal(entropy("0123"), 2, "<code>entropy("0123")</code> should return <code>2</code>");'
  - text: <code>entropy(&quot;01234567&quot;)</code>应该返回<code>3</code>
    testString: 'assert.equal(entropy("01234567"), 3, "<code>entropy("01234567")</code> should return <code>3</code>");'
  - text: <code>entropy(&quot;0123456789abcdef&quot;)</code>应返回<code>4</code>
    testString: 'assert.equal(entropy("0123456789abcdef"), 4, "<code>entropy("0123456789abcdef")</code> should return <code>4</code>");'
  - text: <code>entropy(&quot;1223334444&quot;)</code>应返回<code>1.8464393446710154</code>
    testString: 'assert.equal(entropy("1223334444"), 1.8464393446710154, "<code>entropy("1223334444")</code> should return <code>1.8464393446710154</code>");'

```

</section>

## Challenge Seed
<section id='challengeSeed'>

<div id='js-seed'>

```js
function entropy (s) {
  // Good luck!
}

```

</div>



</section>

## Solution
<section id='solution'>

```js
// solution required
```
</section>