202. Happy Number

/* I use square_digit to get the sume of the square of the digits,
then in the isHappy we build a set, every time the sum obtained by square_digit, we will check if it is in the hashset until the number 
becomes 1. If the number successfully becomes 1, it is a happy number. Otherwise, it shows in the hashset, it will be not a happy number
hashset.add() returns a boolean value, if the item successfully adds in the set, it will return true, otherwise it will return false.

*/
public class Solution {
    public int square_digit(int n)
    {   
    int sum=0;
    int i=0;
        for(i=0;i<32;i++)
        {   int residual=n%10;
        if(n==0)
        break;
            sum+=residual*residual;
            n=n/10;
        }
        return sum;
         
        
    }
    public boolean isHappy(int n) {
        HashSet<Integer> res = new HashSet<Integer>();
        if(n<=0)
        return false;
        
        while(n!=1)
        {
        if(res.add(n))
        n=square_digit(n);
        else
        return false;
        }
        return true;
    }
}
//第二次做的
public class Solution {
    public boolean isHappy(int n) {
        if(n<=0)
        return false;
        Set<Integer> reserve= new HashSet<Integer>();
        while(sqOfDigits(n)!=1)
        {if(!reserve.add(sqOfDigits(n)))
         break;
         n=sqOfDigits(n);    
        }
        return sqOfDigits(n)==1;
    }
    public int sqOfDigits(int n)
    { ArrayList<Integer> sq =new ArrayList<Integer>();
      while(n/10!=0)
      {sq.add(n%10);
       n=n/10;
      } 
      sq.add(n%10);
      int sum=0;
      for (int i=0; i<sq.size();i++)
      sum+=sq.get(i)*sq.get(i);
      return sum;    
      
    }
}