202.happy-number.js

/*
 * @lc app=leetcode id=202 lang=javascript
 *
 * [202] Happy Number
 *
 * https://leetcode.com/problems/happy-number/description/
 *
 * algorithms
 * Easy (44.36%)
 * Total Accepted:    227.2K
 * Total Submissions: 505.7K
 * Testcase Example:  '19'
 *
 * 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: 
 * 1^2 + 9^2 = 82
 * 8^2 + 2^2 = 68
 * 6^2 + 8^2 = 100
 * 1^2 + 0^2 + 0^2 = 1
 * 
 */
function squareSum(n) {
    let sum = 0, tmp;
    while (n) {
        tmp = n % 10;
        sum += tmp * tmp;
        n = Math.floor(n / 10);
    }
    return sum;
}

function isHappyWithMapper(n, visited) {
    if (n === 1) return true;
    if (visited[n]) return false;
    visited[n] = true;

    return isHappyWithMapper(squareSum(n), visited);
}
/**
 * @param {number} n
 * @return {boolean}
 */
var isHappy = function(n) {
    const visited = {};

    return isHappyWithMapper(n, visited);
};