78 lines
1.6 KiB
Markdown
78 lines
1.6 KiB
Markdown
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---
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id: 5900f3941000cf542c50fea7
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title: 'Problem 40: Champernowne''s constant'
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challengeType: 5
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forumTopicId: 302066
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dashedName: problem-40-champernownes-constant
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---
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# --description--
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An irrational decimal fraction is created by concatenating the positive integers:
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0.12345678910**1**112131415161718192021...
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It can be seen that the 12<sup>th</sup> digit of the fractional part is 1.
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If *d<sub>n</sub>* represents the *n*<sup>th</sup> digit of the fractional part, find the value of the following expression.
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d<sub>1</sub> × d<sub>10</sub> × d<sub>100</sub> × d<sub>1000</sub> × d<sub>10000</sub> × d<sub>100000</sub> × d<sub>1000000</sub>
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# --hints--
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`champernownesConstant(100)` should return a number.
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```js
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assert(typeof champernownesConstant(100) === 'number');
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```
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`champernownesConstant(100)` should return 5.
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```js
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assert.strictEqual(champernownesConstant(100), 5);
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```
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`champernownesConstant(1000)` should return 15.
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```js
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assert.strictEqual(champernownesConstant(1000), 15);
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```
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`champernownesConstant(1000000)` should return 210.
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```js
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assert.strictEqual(champernownesConstant(1000000), 210);
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```
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# --seed--
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## --seed-contents--
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```js
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function champernownesConstant(n) {
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return true;
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}
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champernownesConstant(100);
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```
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# --solutions--
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```js
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function champernownesConstant(n) {
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let fractionalPart = '';
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for (let i = 0; fractionalPart.length <= n; i++) {
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fractionalPart += i.toString();
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}
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let product = 1;
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for (let i = 0; i < n.toString().length; i++) {
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const index = 10 ** i;
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product *= parseInt(fractionalPart[index], 10);
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}
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return product;
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}
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```
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