[LeetCode] 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: 19 is a happy number
  • 12 + 92 = 82
  • 82 + 22 = 68
  • 62 + 82 = 100
  • 12 + 02 + 02 = 1

Thought process:
Use a hashset to record every number.

Solution:

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public class Solution {
    public boolean isHappy(int n) {
        Set<Integer> set = new HashSet<>();
        
        while (true) {
            int sum = 0;
            
            while (n > 0) {
                int digit = n % 10;
                sum += digit * digit;
                n /= 10;
            }
            
            if (sum == 1) {
                return true;
            }
            if (set.contains(sum)) {
                return false;
            }
            
            set.add(sum);
            n = sum;
        }
    }
}

Location: Philadelphia, PA, USA

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