Happy Number

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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: 19 is a happy number

12 + 92 = 82
82 + 22 = 68
62 + 82 = 100
12 + 02 + 02 = 1

Tags:

Hash map, Math

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/**
 * @param {number} n
 * @return {boolean}
 */
function isHappyHelper(n, hash) {
    var arr = n.toString().split('');
    var ret = 0;
    for (var i in arr) {
        ret += parseInt(arr[i]) * parseInt(arr[i]);
    }

    if (ret === 1) {
        return true;
    } else {
        if (hash.includes(ret)) {
            return false;
        } else {
            hash.push(ret);
            return isHappyHelper(ret, hash);
        }
    }
}

var isHappy = function (n) {
    return isHappyHelper(n, []);
};

Pay attention to the dictionary "Hash", it will be updated to be [] if we call it recursively.

Pass hash as a parameter will solve the problem.