66 lines
1.1 KiB
Markdown
66 lines
1.1 KiB
Markdown
---
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id: 599d15309e88c813a40baf58
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title: 熵
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challengeType: 5
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videoUrl: ''
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---
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# --description--
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任务：
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计算给定输入字符串的香农熵H.
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给定谨慎的随机变量$ X $，它是$ N $“符号”（总字符）的字符串，由$ n $个不同的字符组成（对于二进制，n = 2），位/符号中X的香农熵是：
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$ H*2（X）= - \\ sum* {i = 1} ^ n \\ frac {count_i} {N} \\ log_2 \\ left（\\ frac {count_i} {N} \\ right）$
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其中$ count_i $是字符$ n_i $的计数。
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# --hints--
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`entropy`是一种功能。
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```js
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assert(typeof entropy === 'function');
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```
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`entropy("0")`应该返回`0`
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```js
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assert.equal(entropy('0'), 0);
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```
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`entropy("01")`应该返回`1`
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```js
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assert.equal(entropy('01'), 1);
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```
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`entropy("0123")`应该返回`2`
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```js
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assert.equal(entropy('0123'), 2);
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```
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`entropy("01234567")`应该返回`3`
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```js
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assert.equal(entropy('01234567'), 3);
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```
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`entropy("0123456789abcdef")`应返回`4`
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```js
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assert.equal(entropy('0123456789abcdef'), 4);
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```
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`entropy("1223334444")`应返回`1.8464393446710154`
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```js
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assert.equal(entropy('1223334444'), 1.8464393446710154);
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```
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# --solutions--
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