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title	id	challengeType
Harshad or Niven series	595668ca4cfe1af2fb9818d4	5

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.

Tests

tests:
  - text: <code>isHarshadOrNiven</code> is a function.
    testString: assert(typeof isHarshadOrNiven === 'function', '<code>isHarshadOrNiven</code> is a function.');
  - text: '<code>isHarshadOrNiven()</code> should return <code>{"firstTwenty": [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 18, 20, 21, 24, 27, 30, 36, 40, 42],"firstOver1000": 1002}</code>'
    testString: assert.deepEqual(isHarshadOrNiven(), res);

Challenge Seed

function isHarshadOrNiven() {
  const res = {
    firstTwenty: [],
    firstOver1000: undefined
  };
  // Change after this line

  return res;
}

After Test

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
};

Solution

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;
}

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