202. Happy Number

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Problem

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 + 02 = 1

Code

class Solution {
    public boolean isHappy(int n) {
        HashSet<Integer> set = new HashSet<>();

        while(n != 1){
            int temp = 0;
            while(n != 0){
                int digit = n % 10;
                temp += digit * digit;
                n /= 10;
            }

            if(!set.add(temp)){
                return false;
            }

            n = temp;
        }

        return true;
    }
}