Question

I’m trying to make my Hailstone sequence output the smallest integer that cannot be computed due to the restrictions on int, but for some reason it still is not working. Any ideas as to why it’s not would be greatly appreciated.

    public static void main(String[] args) {
        int x=2; 
        int count = x;
        //Collatz Conjecture computation
        while (true)
        {   x=2; 
            x =count;
            while (x != 1)
            {   
                if (x % 2 == 0)
                    x = x / 2;
                if (x % 2 == 1)
                    x = x * 3 + 1;
                if (x < 0)
                {   System.out.print("The integer " + count + " cannot have its Hailstone sequence computed using int variables. ");
                    return;
                }
            }
            count ++;
        }
    }

Answer 1

Currently, your Hailstone sequence will reach an unending sequence of 4, 2, 1, 4, 2, 1, ..., because, you are having multiple if's instead of if-else.

You should change your set of if's to: –

if (x % 2 == 0)
    x = x / 2;
else
    x = x * 3 + 1;
if (x < 0) {   
    System.out.print("The integer " + count + " cannot have its Hailstone sequence computed using int variables. ");
    return;
}

---

So, what was the Issue?

If you were using just if's, then at one point of time, your x will become 1 due to first if condition.

So, with x = 1, the 2nd if would be executed, and x would now become – 1 * 3 + 1 = 4. Then the while loop continues. Again, x becomes 2 (1st if), then again while loop continues (As 2nd if is not satisfied now. 2 % 2 != 1), and then x becomes 1 (1st if), then 4 (2nd if), and so on. This problem arise, because both your if blocks was getting executed everytime.

---

Just to complete the answer, I think you don’t even need that last condition – x < 0. Your while loop will automatically break when x becomes 1. And this must be the only condition of ending the sequence. Because, once you start with value 1, you would end up in that deadly sequence. So, just remove if (x < 0) part. Not Needed.

So, you should just use: –

if (x % 2 == 0)
    x = x / 2;
else
    x = x * 3 + 1;

in your inner while.