題目

Write an algorithm to determine if a number n is "happy".

A happy number is a number 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.

Return True if n is a happy number, and False if not.

題意

快樂數(Happy Number)定義是，整數中的每個位數平方後相加，其結果再做同樣的操作，直到結果為1，就是快樂數，若一直循環不是1的話，就不是快樂數。

Example:

Input: 19
Output: true
Explanation:
12 + 92 = 82
82 + 22 = 68
62 + 82 = 100
12 + 02 + 02 = 1

解題想法

設定邊界條件，若小於1，不成立。
若，不等於1，且沒有重複的話就繼續計算，直到結果為1，
n為參數，將n的各位數拆分為陣列s，計算每個位數的平方和：

n = s.map(e => e * e).reduce((acc, cur) => acc + cur);

Solution

var isHappy = function(n) {
let array = [];
  if (n < 1) {
    return false;
  }
  while (n !== 1) {
    let s = ('' + n).split('');
    n = s.map(e => e * e).reduce((acc, cur) => acc + cur);
    if (array.includes(n)) {
      return false
    }
    array.push(n);
  }
  return true;
};