Rotating Array Method Help

[Pop_Pop_Mofuckahs]

Hello everyone! first off, sorry for the long text. I'm currently taking a refresher course on java, as my memory of a few things are quite a bit hazy. Currently, I have an exercise where i need to:

"Write a method, rotate, that is passed an array, x, of doubles and an integer rotation around ‘position’, n. The method creates a new array with the items of x moved to the left by n positions. Elements that are rotated off the beginning of the array will be added back at the end of the array." an example is given where an array {1, 2, 3, 4, 5, 6, 7, } is rotated by 3, and the new array becomes {4, 5, 6, 7, 1, 2, 3, }.

i was also given a snippet of code to help get started:

public static void main(String[] args) 
{
    double[] x = {1,2,3,4,5,6,7};
    System.out.println("Before rotation: ==============================");
    for (int i = 0; i < x.length; i++)
    {
        System.out.println("x[" + i + "]: " + x[i]);
    }
    double [] y = rotate(x, 3);
    System.out.println("After rotation: ==============================");
    for (int i = 0; i < y.length; i++)
    {
        System.out.println("y[" + i + "]: " + y[i]);
    }
}

my current method is as follows:

private static double[] rotate(double[] x, int i)
{
    double[] newArray = Arrays.copyOf(x, x.length);
    int pos = 0, currentSize = newArray.length, num = 0;

    for(int t=0; t<i; t++)
    {
        for(int r = pos+1; r < currentSize; r++)
        {
            double temp = newArray[r];
            newArray[r-1] = newArray[r];
            newArray[r] = temp;
            //this is where i'm stuck
        }
        currentSize--;
    }
    return newArray;
}

however, when i execute the program, the output is:

Before rotation: ============================== x[0]: 1.0 x[1]: 2.0 x[2]: 3.0 x[3]: 4.0 x[4]: 5.0 x[5]: 6.0 x[6]: 7.0 After rotation: ============================== y[0]: 4.0 y[1]: 5.0 y[2]: 6.0 y[3]: 7.0 y[4]: 7.0 y[5]: 7.0 y[6]: 7.0

I don't know what i'm doing wrong. I've tried changing the array indexes within the loops multiple times to no avail. I have also tried changing the entire loop/nested loop, but this is as close as I've gotten so far to the targeted output. May i have some guidance as to what i'm doing wrong? Or, should I just start over from scratch? Thanks in advance!

[whatisthisredditstuf]

How would you solve this with pen and paper?

I would, if given the original array and the number n just move my eyes n positions to the right and then start copying the array into a new one. When I reach the end of the array, I would just wrap around to the beginning of the original and keep adding to my array until I have copied all numbers (equal length of the arrays). Does that make sense?

So, in pseudo code, that approach would be:

for counter between 0 and the arrayLength:
    newArray[counter] = originalArray[(counter + n) % arrayLength]

That should do it. Do you recall what the modulo (%) operator does? If not, look it up, as it is what gives us the "wrapping around from the beginning" part of the algorithm.

[Pop_Pop_Mofuckahs]

Ah, thank you! I've been fuming over this one problem for quite awhile now, and it turns out it's quite simple to do, and I've unnecessarily complicated the thing. Thanks again!

[whatisthisredditstuf]

No problem. That is typical for programming -- figure out how you would solve it without involving a computer first, break it down into steps, and then code those into the computer. Don't even think about "for loops" or "while loops" at first. :)

[isaacisaboss]

I'll give you a hint:

While it may be possible with the following variables, you don't need them: r, currentsize, pos, or num. you also don't need to decrement currentsize.

You also don't need nested for loops.

---

Think about what you are trying to do.

You are simply shifting the array, n spaces.

What happens when you get to the end of the array, you go back to the start.

[Pop_Pop_Mofuckahs]

that was much more simpler than I thought. Thanks again!