# Rearrange first N numbers to make them at 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.

**Examples :**

Input : N = 12 K = 2 Output : [3 4 1 2 7 8 5 6 11 12 9 10] Explanation : Initial permutation is [1 2 3 4 5 6 7 8 9 10 11 12] In rearrangement, [3 4 1 2 7 8 5 6 11 12 9 10] we have all elements at distance 2. Input : N = 12 K = 3 Output : [4 5 6 1 2 3 10 11 12 7 8 9]

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.

## C++

`// C++ program to rearrange permuatations to make ` `// them K distance away ` `#include <bits/stdc++.h> ` `using` `namespace` `std; ` ` ` `/* Method prints permutation of first N numbers, ` `where each number is K distance away from its ` `actual position */` `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] << ` `" "` `; ` `} ` ` ` `// Driver code ` `int` `main() ` `{ ` ` ` `int` `N = 12, K = 3; ` ` ` `printRearrangeNnumberForKDistance(N, K); ` ` ` `return` `0; ` `} ` |

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## Java

`// Java program to rearrange permuatations ` `// to make them K distance away ` ` ` `class` `GFG ` `{ ` ` ` `/* Method prints permutation of first N numbers, ` ` ` `where each number is K distance away from its ` ` ` `actual position */` ` ` `static` `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++) ` ` ` `System.out.print(i + ` `" "` `); ` ` ` `System.out.println(); ` ` ` `return` `; ` ` ` `} ` ` ` ` ` `// If N doesn't divide (2K) evenly, then ` ` ` `// rearrangement is not possible ` ` ` `if` `(N % (` `2` `* K) != ` `0` `) ` ` ` `{ ` ` ` `System.out.print(` `"Not Possible\n"` `); ` ` ` `return` `; ` ` ` `} ` ` ` ` ` `// Copy first N numbers to an auxiliary ` ` ` `// array ` ` ` `int` `arr[]=` `new` `int` `[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++) ` ` ` `{ ` ` ` `int` `temp = arr[i + j - ` `1` `]; ` ` ` `arr[i + j - ` `1` `] = arr[K + i + j - ` `1` `]; ` ` ` `arr[K + i + j - ` `1` `] = temp; ` ` ` `} ` ` ` ` ` `// Print the rearranged array ` ` ` `for` `(` `int` `i = ` `1` `; i <= N; i++) ` ` ` `System.out.print(arr[i] + ` `" "` `); ` ` ` `} ` ` ` ` ` `// Driver code ` ` ` `public` `static` `void` `main (String[] args) ` ` ` `{ ` ` ` `int` `N = ` `12` `, K = ` `3` `; ` ` ` `printRearrangeNnumberForKDistance(N, K); ` ` ` `} ` `} ` ` ` `// This code is contributed by Anant Agarwal. ` |

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## C#

`// C# program to rearrange permuatations ` `// to make them K distance away ` `using` `System; ` ` ` `class` `GFG ` `{ ` ` ` `/* Method prints permutation of first N numbers, ` ` ` `where each number is K distance away from its ` ` ` `actual position */` ` ` `static` `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++) ` ` ` `Console.Write(i + ` `" "` `); ` ` ` `Console.WriteLine(); ` ` ` `return` `; ` ` ` `} ` ` ` ` ` `// If N doesn't divide (2K) evenly, then ` ` ` `// rearrangement is not possible ` ` ` `if` `(N % (2 * K) != 0) ` ` ` `{ ` ` ` `Console.Write(` `"Not Possible\n"` `); ` ` ` `return` `; ` ` ` `} ` ` ` ` ` `// Copy first N numbers to an auxiliary ` ` ` `// array ` ` ` `int` `[]arr=` `new` `int` `[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++) ` ` ` `{ ` ` ` `int` `temp = arr[i + j - 1]; ` ` ` `arr[i + j - 1] = arr[K + i + j - 1]; ` ` ` `arr[K + i + j - 1] = temp; ` ` ` `} ` ` ` ` ` `// Print the rearranged array ` ` ` `for` `(` `int` `i = 1; i <= N; i++) ` ` ` `Console.Write(arr[i] + ` `" "` `); ` ` ` `} ` ` ` ` ` `// Driver code ` ` ` `public` `static` `void` `Main () ` ` ` `{ ` ` ` `int` `N = 12, K = 3; ` ` ` `printRearrangeNnumberForKDistance(N, K); ` ` ` `} ` `} ` ` ` `// This code is contributed by nitin mittal. ` |

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**Output :**

4 5 6 1 2 3 10 11 12 7 8 9

This article is contributed by **Utkarsh Trivedi**. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

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