Algorithm Misc - Finding patterns

http://www.geeksforgeeks.org/rearrange-first-n-numbers-make-k-distance/
Given a positive number K, we need to permute first N natural numbers in such a way that absolute distance of each permuted number from its original position is K and if it is not possible to rearrange them in such manner then print not possible.

We can solve this problem by finding the pattern in solutions. If we go through many solutions manually, we can see that if we partition N numbers into slots of size 2K, then each slot can be rearranged in two parts of size K, where the difference of position with actual position will be K.

Example 1 : N = 12 and K = 2

First 12 numbers are partitioned into 
2*2 = 4 sized 12/4 = 3 slots as shown below,
[[1 2 3 4] [5 6 7 8] [9 10 11 12]]

Now each half of the slot is swapped so that, 
every number will go at K position distance 
from its initial position as shown below,
[[3 4 1 2] [7 8 5 6] [11 12 9 10]]

Example 2 :  N = 12 and K = 3,
[1 2 3 4 5 6 7 8 9 10 11 12]
[[1 2 3 4 5 6] [7 8 9 10 11 12]]
[[4 5 6 1 2 3] [10 11 12 7 8 9]]
[4 5 6 1 2 3 10 11 12 7 8 9]
Which is the final rearrangement for 
N = 12 and K = 3

In below code, the case when K = 0 is handled separately by printing all numbers in their actual order. When N is not divisible by 2K, ‘not possible’ is printed directly.

void printRearrangeNnumberForKDistance(int N, int K)

{

    // If K = 0, then print numbers in their natural

    // order

    if (K == 0)

    {

        for (int i = 1; i <= N; i++)

            cout << i << " ";

        cout << endl;

        return;

    }

    // If N doesn't divide (2K) evenly, then

    // rearrangement is not possible

    if (N % (2 * K) != 0)

    {

        cout << "Not Possible\n";

        return;

    }

    // Copy first N numbers to an auxiliary

    // array

    int arr[N + 1];

    for (int i = 1; i <= N; i++)

        arr[i] = i;

    // Swap halves of each 2K sized slot

    for (int i = 1; i <= N; i += 2*K)

        for (int j = 1; j <= K; j++)

            swap(arr[i+j-1], arr[K+i+j-1]);

    // Print the rearranged array

    for (int i = 1; i <= N; i++)

        cout << arr[i] << " ";

}