Java solution

[TravisZeng]

store all calculating numbers in a hashset and check every time if we are in a cycle

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