Question

I want to generate random numbers within a range and the generated numbers should not collide within some range.
i used following code but im getting Stackoverflow error.. Any better solution?

static int [] xPositions=new int[10];
int WIDTH=700
public static void main(String args[])throws IOException
{

    if(generateRandomXPositions(10)){
        for(int i=0;i<10;i++){
          System.out.println(" Random Numbers "+i+"  :"+xPositions[i]);
        }
    }


}

private static boolean generateRandomXPositions(int n) {

    for(int i=0;i<10;i++){
        int temp=((int)0 + (int)(Math.random() * ((WIDTH - 0) + 1)));
        for(int j=0;j<xPositions.length;j++){
            if(xPositions[j]>temp-50 && xPositions[j]<temp+50){ // IF GENERATED NUMBER IS IN THIS RANGE IT SHOULD REGENERATE THE NUMBERS 
                generateRandomXPositions(10); 
            }
        }
        xPositions[i]=temp;
    }
    return true;
}

I know problem is here

if(xPositions[j]>temp-50 && xPositions[j]<temp+50).   

Below one works fine

`if(xPositions[j]==temp)`.  

But I need that random numbers should follow that range! .

Many are wondering about the exit condition of recursive loop. But I believe if random number is not in that range, then there is no point of entering in to the recursive loop.

UPDATE 1:

And I believe compiler is tired to find the number between this range! Now I found that it is impossible fit 10 images having width of 100px each in to the 700px width container without colliding X positions!

Please see the image below. Lets imagine i want to place this boxes randomly without colliding… how can i do that?

Answer 1

You’re getting a StackOverflowError because the chances of xPositions[j]>temp-50 && xPositions[j]<temp+50 not passing is very low when there’s a range of 50. The chances of this function terminating is even lower due to the inner for-loop. Thus, this will keep recursing..

However, it doesn’t seem like you’re doing what you actually want to accomplish. If you want to generate numbers that are all within a set range, you don’t want to compare xPositions[j] to temp-50 and temp+50. That’s going to regenerate numbers when xPositions[j] isn’t within some random range.

---

If you really just want to generate numbers that are within a certain range, then you’ll want to get rid of the inner for-loop and instead do something like this:

for every number in xPositions:
  a = random number
  if a is within an unwanted range, regenerate numbers
  else set xPositions[i] = a

or without recursion:

for every number in xPositions:
  a = random number
  while a is within an unwanted range:
    a = random number
  set xPositions[i] = a

---

On the other hand, if you want to randomize the order of some images along the x-axis, you can do something like this:

bag = [0 1 2 ... n-1]
shuffle bag
for every number in xPositions:
  xPositions[i] = bag.pop * IMAGE_WIDTH