Question

hi guys, I don't know what I'm doing wrong, can you guys please help me?
Given the rules for a sequence:
If n is even: n = n / 2
If n is odd: n = 3n + 1

For example, if the starting number is 5 the sequence is:
5 -> 16 -> 8 -> 4 -> 2 -> 1

Find the largest starting number under ten million that will generate the longest run of this sequence and ends in 1. 12 years ago

Answer 1

System.out.print("Till which number would you like to decode this sequence?");
Scanner x1 = new Scanner(System.in);
int input = x1.nextInt();
System.out.print("Your number is"+input);
for (int x = 1; x < input ; x += 2){
int y;
y = (x * 3) +1;
while (y<input){
int z ;
z = y/2;
if(z > 1)
while (z>1){
z = y/2;}
if (z < 1)
break;
if (z==1)
break;
System.out.print(+z);
}

}}}

Answer 2

What am I doing wrong?

Answer 3

To start with, your sequence will never evaluate an odd number.
You start x at 1, then you add 2 for every iteration, so you are always stepping up odd numbers. Then you multiply by 3 and add 1, so y is always even. Since you run the evaluation on z, which is just y divided by 2, you are always working on an even increment.
You could find your odd/even numbers more efficiently if you take your value and mod it by 2. For example:
5%2 = 1
6%2 = 0
25%2 = 1
100%2 = 0

As for your sequence, you are never generating one. Take an input of 10, your output for x,y,z would be:
var 1st iteration 2nd iteration 3rd iteration 4th iteration 5th iteration
x 1 3 5 7 9
y 4 10 16 22 28
z 2,1 5,2,1 8,4,2,1 11,5,2,1 14,7,3,1

Answer 4

Well the 3rd iteration worked, correct? 5>16>8,4,2,1. So that's what I want, except the largest possible value.

Answer 5

I set it so it will only print if it comes up.

And how come when I enter this in the program, it doesn't display an answer for me?

Answer 6

The iterations that I laid out were based on the mathematical logic you were using. I was attempting to avoid compiling your code as I was not clear on the end goal you were after. That said, I have compiled your code and you have a couple of infinite loops.
1. Your 'while' is true for as long as 'y<input' and yet the value of 'y' is never changed
while (y<input){
int z ;
z = y/2;
if(z > 1) while (z>1){
z = y/2;
}
if (z < 1) break;
if (z==1) break;
System.out.print(+z);
}
2. Your 'if' is true 'while' z>1, since 'y' is never changed, 'z' is never changed. This is where your program sticks.
if(z > 1) while (z>1){
z = y/2;
}

Answer 7

If your desired output is something like this:
Till which number would you like to decode this sequence?5
Your number is 5
16
8
4
2
1

I would suggest code similar to this:
int x;
x = input;

while(x>1){
if (x%2 == 0){
x = (x/2);
}
else if (x%2 == 1){
x = (x * 3) + 1;
}
System.out.println(x);
}