Happy Number

LeetCode Q 202 - Happy Number

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

Solution

Code:

public boolean isHappy(int n) {
	Set<Integer> seen = new HashSet<>();
	while (n != 1) {
		if (seen.contains(n)) return false;
		seen.add(n);
		n = helper(n);
	}
	return true;
}

private int helper(int n) {
	int res = 0;
	while (n != 0) {
		res += (n % 10) * (n % 10); // (n % 10) ^ 2 is not correct
		n /= 10;
	}
	return res;
}