LeetCode 202. Happy Number (javascript)

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.
• 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.

Return true if n is a happy number, and false if not.

Example 1:

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

Example 2:

Input: n = 2
Output: false

Constraints:

• 1 <= n <= 231 - 1

Idea:

create a function to calculate the sum of the squares of its digits.

use fast and slow pointers traversal concept (the other one execute function twice) to check if they can reach 1 (means it is happy number)

Solution:

/**
 * @param {number} n
 * @return {boolean}
 */
var isHappy = function(n) {
    let slow = n;
    let fast = n;
    
    do {
        slow = squareSum(slow);
        fast = squareSum(squareSum(fast));
    } while (slow !== fast);
    
    return fast === 1;
};

var squareSum = function(n) {
    let sum = 0;
    while(n) {
        sum += (n % 10) * (n % 10);
        n = parseInt(n / 10);
    }
    return sum;
};