freeCodeCamp/curriculum/challenges/chinese/10-coding-interview-prep/rosetta-code/hailstone-sequence.md

id, title, challengeType, forumTopicId, dashedName

id	title	challengeType	forumTopicId	dashedName
595608ff8bcd7a50bd490181	Hailstone sequence	1	302279	hailstone-sequence

--description--

Hailstone 数字序列可以从一个起始正整数 n 生成：

• If n is 1 then the sequence ends
• If n is even then the next n of the sequence = n/2
• If n is odd then the next n of the sequence = (3 * n) + 1

The (unproven) Collatz conjecture is that the hailstone sequence for any starting number always terminates.

The hailstone sequence is also known as hailstone numbers (because the values are usually subject to multiple descents and ascents like hailstones in a cloud), or as the Collatz sequence.

--instructions--

1. Create a routine to generate the hailstone sequence for a number
2. Your function should return an array with the number less than limit which has the longest hailstone sequence and that sequence's length. (But don't show the actual sequence!)

--hints--

hailstoneSequence 应该是一个函数。

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

hailstoneSequence(30) should return an array.

assert(Array.isArray(hailstoneSequence(30)));

hailstoneSequence(30) should return [27, 112].

assert.deepEqual(hailstoneSequence(30), [27, 112]);

hailstoneSequence(50000) should return [35655, 324].

assert.deepEqual(hailstoneSequence(50000), [35655, 324]);

hailstoneSequence(100000) should return [77031, 351].

assert.deepEqual(hailstoneSequence(100000), [77031, 351]);

--seed--

--seed-contents--

function hailstoneSequence(limit) {
  const res = [];


  return res;
}

--solutions--

function hailstoneSequence (limit) {
  function hailstone(n) {
    const seq = [n];
    while (n > 1) {
      n = n % 2 ? 3 * n + 1 : n / 2;
      seq.push(n);
    }
    return seq;
  }

  let n = 0;
  let max = 0;
  for (let i = limit; --i;) {
    const seq = hailstone(i);
    const sLen = seq.length;

    if (sLen > max) {
      n = i;
      max = sLen;
    }
  }

  return [n, max];
}