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 + 0^2 = 1

Solution

Code:

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

private int getNextNumber(int n) {
  int res = 0;
  while (n != 0) {
    res += (n % 10) ^ (n % 10);
    n /= 10;
  }
  return res;
}