Java – how to invert large arrays?

OK, so I know it's very easy to reverse the array by swapping items until you reach the middle like this:

int array[SIZE];
int temp;

for (int i = 0; i < SIZE/2; i++)
  {
     temp = array[i];
     array[i] = array[SIZE-1 - i];
     array[SIZE-1 - i] = temp;
  }

But what if the array size is really as big as 10000? Is it possible to do o (n)?

Solution

You can't complete it faster than the current algorithm you run in O (n) You may be interested in wrapping arrays in classes that provide o (1) inversion:

A simple version might look like this:

public class ReversableArray {
  private boolean reverse = false;
  private final int[] array;
  public ReversableArray(int[] array) { this.array = array; }

  public int get(int index) {
    return reverse ? array[array.length - index - 1] : array[index];
  }
  public void reverse() { reverse = !reverse; }
}