LeetCode 202. Happy Number

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: 19 is a happy number

  • 12 + 92 = 82
  • 82 + 22 = 68
  • 62 + 82 = 100
  • 12 + 02 + 02 = 1

Credits:
Special thanks to @mithmatt and @ts for adding this problem and creating all test cases.

Solution:

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

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