freeCodeCamp/curriculum/challenges/en/08-coding-interview-prep/rosetta-code/happy-numbers.en.md

title, id, challengeType

title	id	challengeType
Happy numbers	594810f028c0303b75339ad1	5

Description

A happy number is defined by the following process:

Starting with any positive integer, replace the number by the sum of the squares of its digits, and repeat the process until the number equals 1 (where it will stay), or it loops endlessly in a cycle which does not include 1. Those numbers for which this process ends in 1 are happy numbers, while those that do not end in 1 are unhappy numbers.

Implement a function that returns true if the number is happy, or false if not.

Instructions

Tests

- text: <code>happy</code> is a function.
  testString: 'assert(typeof happy === ''function'', ''<code>happy</code> is a function.'');'
- text: <code>happy(1)</code> should return a boolean.
  testString: 'assert(typeof happy(1) === ''boolean'', ''<code>happy(1)</code> should return a boolean.'');'
- text: <code>happy(1)</code> should return true.
  testString: 'assert(happy(1), ''<code>happy(1)</code> should return true.'');'
- text: <code>happy(2)</code> should return false.
  testString: 'assert(!happy(2), ''<code>happy(2)</code> should return false.'');'
- text: <code>happy(7)</code> should return true.
  testString: 'assert(happy(7), ''<code>happy(7)</code> should return true.'');'
- text: <code>happy(10)</code> should return true.
  testString: 'assert(happy(10), ''<code>happy(10)</code> should return true.'');'
- text: <code>happy(13)</code> should return true.
  testString: 'assert(happy(13), ''<code>happy(13)</code> should return true.'');'
- text: <code>happy(19)</code> should return true.
  testString: 'assert(happy(19), ''<code>happy(19)</code> should return true.'');'
- text: <code>happy(23)</code> should return true.
  testString: 'assert(happy(23), ''<code>happy(23)</code> should return true.'');'
- text: <code>happy(28)</code> should return true.
  testString: 'assert(happy(28), ''<code>happy(28)</code> should return true.'');'
- text: <code>happy(31)</code> should return true.
  testString: 'assert(happy(31), ''<code>happy(31)</code> should return true.'');'
- text: '<code>happy(32)</code> should return true:.'
  testString: 'assert(happy(32), ''<code>happy(32)</code> should return true:.'');'
- text: <code>happy(33)</code> should return false.
  testString: 'assert(!happy(33), ''<code>happy(33)</code> should return false.'');'

Challenge Seed

function happy (number) {
  // Good luck!
}

Solution

function happy (number) {
  let m;
  let digit;
  const cycle = [];

  while (number !== 1 && cycle[number] !== true) {
    cycle[number] = true;
    m = 0;
    while (number > 0) {
      digit = number % 10;
      m += Math.pow(digit, 2);
      number = (number - digit) / 10;
    }
    number = m;
  }
  return (number === 1);
}