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

My Solution

class Solution {
    public boolean isHappy(int n) {
        int sum = 0, x = n;
        Set<Integer> set = new HashSet<Integer>();
        while (sum != 1 || x != 0) {
            if (x != 0) {
                sum += Math.pow(x % 10, 2);
                x /= 10;
            } else {
                if (set.contains(sum)) {
                    return false;
                } else {
                    set.add(sum);
                    x = sum;
                    sum = 0;
                }
            }
        }
        return true;
    }
}

Great Solution

public class Solution {
    public boolean isHappy(int n) {
        int x = n;
        int y = n;
        while(x>1){
            x = cal(x) ;
            if(x==1) return true ;
            y = cal(cal(y));
            if(y==1) return true ;

            if(x==y) return false;
        }
        return true ;
    }
    public int cal(int n){
        int x = n;
        int s = 0;
        while(x>0){
            s = s+(x%10)*(x%10);
            x = x/10;
        }
        return s ;
    }
}