[Algorithm] 202. Happy Number

Write an algorithm to determine if a number 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.

Example: 

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

 

Handle the number directly, common way is thougth % or / operator

/**
 * @param {number} n
 * @return {boolean}
 */
var isHappy = function(n) {
    let memo = {};
    
    while(n !== 1 && !memo[n]) {
        memo[n] = true;
        let sum = 0;
        while(n > 0) {
            sum += (n % 10) *(n % 10);
            n = Math.floor(n / 10);
        }
        n = sum;
    }
    
    return n == 1;
};

 

Second way:

/**
 * @param {number} n
 * @return {boolean}
 */
var isHappy = function(n) {
    return helper(n, {});
};

function helper(n, memo) {
    const ary = `${n}`.split('');
    let sum = 0;
    for (let n of ary) {
        sum += Math.pow(parseInt(n, 10), 2);
    }
    
    if (sum === 1) {
        return true;
    }
    
    if (sum in memo) {
        return false;
    }
    memo[sum] = true;
    return helper(sum, memo);
}