0202 - Happy Number

0202 - Happy Number

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.

Examples

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

Input: n = 2 Output: false

Constraints

• 1 <= n <= 231 - 1

Java Solution

class Solution {
    public boolean isHappy(int n) {
        Set<Integer> seen = new HashSet<>();
        
        while(n != 1 && !seen.contains(n)) {
            seen.add(n);
            n = helper(n);
        }
        
        return n == 1;
    }
    
    private int helper(int n) {
        int sum = 0;
        
        while(n > 0) {
            int digit = n % 10;
            n = n / 10;
            sum += digit * digit;
        }
        
        
        return sum;
    }
}