freeCodeCamp/curriculum/challenges/english/10-coding-interview-prep/rosetta-code/zeckendorf-number-representation.md

id, title, challengeType, forumTopicId, dashedName

id	title	challengeType	forumTopicId	dashedName
594810f028c0303b75339ad6	Zeckendorf number representation	5	302346	zeckendorf-number-representation

--description--

Just as numbers can be represented in a positional notation as sums of multiples of the powers of ten (decimal) or two (binary); all the positive integers can be represented as the sum of one or zero times the distinct members of the Fibonacci series. Recall that the first six distinct Fibonacci numbers are: 1, 2, 3, 5, 8, 13.

The decimal number eleven can be written as 0*13 + 1*8 + 0*5 + 1*3 + 0*2 + 0*1 or 010100 in positional notation where the columns represent multiplication by a particular member of the sequence. Leading zeroes are dropped so that 11 decimal becomes 10100. 10100 is not the only way to make 11 from the Fibonacci numbers however 0*13 + 1*8 + 0*5 + 0*3 + 1*2 + 1*1 or 010011 would also represent decimal 11. For a true Zeckendorf number there is the added restriction that no two consecutive Fibonacci numbers can be used which leads to the former unique solution.

--instructions--

Write a function that generates and returns an array of the first n Zeckendorf numbers in order.

--hints--

zeckendorf should be function.

assert.equal(typeof zeckendorf, 'function');

Your zeckendorf function should return the correct answer.

assert.deepEqual(answer, solution20);

--seed--

--after-user-code--

const range = (m, n) => (
  Array.from({
    length: Math.floor(n - m) + 1
  }, (_, i) => m + i)
);

const solution20 = [
  '1', '10', '100', '101', '1000', '1001', '1010', '10000', '10001',
  '10010', '10100', '10101', '100000', '100001', '100010', '100100', '100101',
  '101000', '101001', '101010'
];

const answer = range(1, 20).map(zeckendorf);

--seed-contents--

function zeckendorf(n) {

}

--solutions--

// zeckendorf :: Int -> String
function zeckendorf(n) {
  const f = (m, x) => (m < x ? [m, 0] : [m - x, 1]);
  return (n === 0 ? ([0]) :
    mapAccumL(f, n, reverse(
      tail(fibUntil(n))
    ))[1]).join('');
}

// fibUntil :: Int -> [Int]
let fibUntil = n => {
  const xs = [];
  until(
      ([a]) => a > n,
      ([a, b]) => (xs.push(a), [b, a + b]), [1, 1]
  );
  return xs;
};

let mapAccumL = (f, acc, xs) => (
  xs.reduce((a, x) => {
    const pair = f(a[0], x);

    return [pair[0], a[1].concat(pair[1])];
  }, [acc, []])
);

let until = (p, f, x) => {
  let v = x;
  while (!p(v)) v = f(v);
  return v;
};

const tail = xs => (
   xs.length ? xs.slice(1) : undefined
);

const reverse = xs => xs.slice(0).reverse();