freeCodeCamp/curriculum/challenges/english/10-coding-interview-prep/project-euler/problem-40-champernownes-constant.md

id, title, challengeType, forumTopicId, dashedName

id	title	challengeType	forumTopicId	dashedName
5900f3941000cf542c50fea7	Problem 40: Champernowne's constant	5	302066	problem-40-champernownes-constant

--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

--hints--

champernownesConstant(100) should return a number.

assert(typeof champernownesConstant(100) === 'number');

champernownesConstant(100) should return 5.

assert.strictEqual(champernownesConstant(100), 5);

champernownesConstant(1000) should return 15.

assert.strictEqual(champernownesConstant(1000), 15);

champernownesConstant(1000000) should return 210.

assert.strictEqual(champernownesConstant(1000000), 210);

--seed--

--seed-contents--

function champernownesConstant(n) {

  return true;
}

champernownesConstant(100);

--solutions--

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;
}