freeCodeCamp/problem-40-champernownes-constant.english.md at c5a087f8b734f9eff9ad6966014d3f6cc88f7034

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Kristofer Koishigawa 6cfd0fc503 fix: improve Project Euler descriptions, challenge seeds, and test cases (#38016 )

* fix: improve Project Euler descriptions and test case

Improve formatting of Project Euler test descriptions. Also add poker hands array and new test case for problem 54

* feat: add typeof tests and gave functions proper names for first 100 challenges

* fix: continue fixing test descriptions and adding "before test" sections

* fix: address review comments

* fix: adjust grids in 18 and 67 and fix some text that reference files rather than the given arrays

* fix: implement bug fixes and improvements from review

* fix: remove console.log statements from seed and solution

2020-02-28 06:39:47 -06:00

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id, challengeType, title, forumTopicId

id	challengeType	title	forumTopicId
5900f3941000cf542c50fea7	5	Problem 40: Champernowne's constant	302066

Description

An irrational decimal fraction is created by concatenating the positive integers:

0.123456789101112131415161718192021...

It can be seen that the 12^th digit of the fractional part is 1.

If d_n represents the n^th digit of the fractional part, find the value of the following expression.

d₁ × d₁₀ × d₁₀₀ × d₁₀₀₀ × d₁₀₀₀₀ × d₁₀₀₀₀₀ × d_1000000

Instructions

Tests

tests:
  - text: <code>champernownesConstant(100)</code> should return a number.
    testString: assert(typeof champernownesConstant(100) === 'number');
  - text: <code>champernownesConstant(100)</code> should return 5.
    testString: assert.strictEqual(champernownesConstant(100), 5);
  - text: <code>champernownesConstant(1000)</code> should return 15.
    testString: assert.strictEqual(champernownesConstant(1000), 15);
  - text: <code>champernownesConstant(1000000)</code> should return 210.
    testString: assert.strictEqual(champernownesConstant(1000000), 210);

Challenge Seed

function champernownesConstant(n) {
  // Good luck!
  return true;
}

champernownesConstant(100);

Solution

function champernownesConstant(n) {
  let fractionalPart = '';
  for (let i = 0; fractionalPart.length <= n; i++) {
    fractionalPart += i.toString();
  }

  let product = 1;
  for (let i = 0; i < n.toString().length; i++) {
    const index = 10 ** i;
    product *= parseInt(fractionalPart[index], 10);
  }

  return product;
}

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