happyNumber.java

// Write an algorithm to determine if a number n 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.

// Return True if n is a happy number, and False if not.

// Example: 

// Input: 19
// Output: true
// Explanation: 
// 12 + 92 = 82
// 82 + 22 = 68
// 62 + 82 = 100
// 12 + 02 + 02 = 1

class Solution {
    public boolean isHappy(int n) {

      HashSet<Integer> h=new HashSet<>(); 
        while(n!=1)
        {
            int c=n;
            int x;
            int sum=0;
            while(c>0)
            {
                x=c%10;
                sum+=Math.pow(x,2);
                c=c/10;
            }
            if(h.contains(sum))
            {
                return false;
            }
            h.add(sum);
            n=sum;
        }
        return true;
    }
}