freeCodeCamp/curriculum/challenges/english/10-coding-interview-prep/rosetta-code/harshad-or-niven-series.md

id, title, challengeType, forumTopicId, dashedName

id	title	challengeType	forumTopicId	dashedName
595668ca4cfe1af2fb9818d4	Harshad or Niven series	5	302281	harshad-or-niven-series

--description--

The Harshad or Niven numbers are positive integers ≥ 1 that are divisible by the sum of their digits.

For example, 42 is a Harshad number as 42 is divisible by (4 + 2) without remainder.

Assume that the series is defined as the numbers in increasing order.

--instructions--

Implement a function to generate successive members of the Harshad sequence.

Use it to list the first twenty members of the sequence and list the first Harshad number greater than 1000.

--hints--

isHarshadOrNiven should be a function.

assert(typeof isHarshadOrNiven === 'function');

isHarshadOrNiven() should return {"firstTwenty": [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 18, 20, 21, 24, 27, 30, 36, 40, 42],"firstOver1000": 1002}

assert.deepEqual(isHarshadOrNiven(), res);

--seed--

--after-user-code--

const res = {
  firstTwenty: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 18, 20, 21, 24, 27, 30, 36, 40, 42],
  firstOver1000: 1002
};

--seed-contents--

function isHarshadOrNiven() {
  const res = {
    firstTwenty: [],
    firstOver1000: undefined
  };
  // Only change code below this line

  return res;
}

--solutions--

function isHarshadOrNiven() {
  const res = {
    firstTwenty: [],
    firstOver1000: undefined
  };

  function isHarshad(n) {
    let s = 0;
    const nStr = n.toString();
    for (let i = 0; i < nStr.length; ++i) {
      s += parseInt(nStr.charAt(i), 10);
    }
    return n % s === 0;
  }

  let count = 0;
  const harshads = [];

  for (let n = 1; count < 20; ++n) {
    if (isHarshad(n)) {
      count++;
      harshads.push(n);
    }
  }

  res.firstTwenty = harshads;

  let h = 1000;
  while (!isHarshad(++h));
  res.firstOver1000 = h;

  return res;
}