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

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