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happyNumber.js
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happyNumber.js
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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:
*
* Input: 19
* Output: true
* Explanation:
* 12 + 92 = 82
* 82 + 22 = 68
* 62 + 82 = 100
* 12 + 02 + 02 = 1
*/
/**
* @param {number} n
* @return {boolean}
*/
var isHappy = function(n) {
// "repeatingNumberChecker" is a hashmap that stores each incoming value that we check for. this
// is to guard against the endless loop (ex. say 101 is a number that will never lead to true, it would loop back to 101 at some point during the endless cycle. this is to skip out if that happens)
let repeatingNumberChecker = {};
let result = n;
// only continue looping if repeatingNumberChecker[result] is false, since
// we're flagging repeatingNumberChecker[result] to true everytime we process a number "result"
while(!repeatingNumberChecker[result]){
if (result === 1){ return true;}
repeatingNumberChecker[result] = true;
let numAsString = result + "",
sumForNumber = 0;
for(let ii=0;ii<numAsString.length;ii++){
let digit = parseInt(numAsString[ii]);
sumForNumber += Math.pow(digit, 2);
}
result = sumForNumber;
}
return false;
};