202. Happy number

subject : Write an algorithm to judge a number n Is it a happy number .

「 Happy number 」  Defined as ：

For a positive integer , Replace the number with the sum of the squares of the numbers in each of its positions .
Then repeat the process until the number becomes 1, It could be Infinite loop But it doesn't change 1.
If this process The result is  1, So this number is the happy number .
If n yes Happy number Just go back to true ; No , Then return to false .

analysis :

The most important thing in this problem is to find the condition to end the cycle .

1)sum==1, End of cycle ,return true;

2)sum When repeated , End of cycle ,return false;

Code (java):

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