# Reverse an array in groups of given size | Set 2 (Variations of Set 1 )

• Difficulty Level : Easy
• Last Updated : 25 Jun, 2021

Given an array, reverse every sub-array that satisfies the given constraints.
We have discussed a solution where we reverse every sub-array formed by consecutive k elements in Set 1. In this set, we will discuss various interesting variations of this problem.

Variation 1 (Reverse Alternate Groups):
Reverse every alternate sub-array formed by consecutive k elements.

Examples:

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```Input:
arr = [1, 2, 3, 4, 5, 6, 7, 8, 9]
k = 3
Output:
[3, 2, 1, 4, 5, 6, 9, 8, 7]

Input:
arr = [1, 2, 3, 4, 5, 6, 7, 8]
k = 2
Output:
[2, 1, 3, 4, 6, 5, 7, 8]```

Below is the implementation –

## C++

 `// C++ program to reverse every alternate sub-array``// formed by consecutive k elements``#include ``using` `namespace` `std;` `// Function to reverse every alternate sub-array``// formed by consecutive k elements``void` `reverse(``int` `arr[], ``int` `n, ``int` `k)``{``    ``// increment i in multiples of 2*k``    ``for` `(``int` `i = 0; i < n; i += 2*k)``    ``{``        ``int` `left = i;` `        ``// to handle case when 2*k is not multiple of n``        ``int` `right = min(i + k - 1, n - 1);` `        ``// reverse the sub-array [left, right]``        ``while` `(left < right)``            ``swap(arr[left++], arr[right--]);``    ``}   ``}` `// Driver code``int` `main()``{``    ``int` `arr[] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14};``    ``int` `k = 3;` `    ``int` `n = ``sizeof``(arr) / ``sizeof``(arr);` `    ``reverse(arr, n, k);` `    ``for` `(``int` `i = 0; i < n; i++)``        ``cout << arr[i] << ``" "``;` `    ``return` `0;``}`

## Java

 `// Java program to reverse``// every alternate sub-array``// formed by consecutive k elements``class` `GFG``{` `// Function to reverse every``// alternate sub-array formed``// by consecutive k elements``    ``static` `void` `reverse(``int` `arr[], ``int` `n, ``int` `k)``    ``{``        ` `        ``// increment i in multiples of 2*k``        ``for` `(``int` `i = ``0``; i < n; i += ``2` `* k)``        ``{``            ``int` `left = i;` `            ``// to handle case when 2*k is not multiple of n``            ``int` `right = Math.min(i + k - ``1``, n - ``1``);` `            ``// reverse the sub-array [left, right]``            ``while` `(left < right) {``                ``swap(arr, left++, right--);``            ``}``        ``}``    ``}` `    ``static` `int``[] swap(``int``[] array, ``int` `i, ``int` `j)``    ``{``        ``int` `temp = array[i];``        ``array[i] = array[j];``        ``array[j] = temp;``        ``return` `array;``    ``}` `    ``// Driver code``    ``public` `static` `void` `main(String[] args)``    ``{``        ``int` `arr[] = {``1``, ``2``, ``3``, ``4``, ``5``, ``6``, ``7``, ``8``,``                    ``9``, ``10``, ``11``, ``12``, ``13``, ``14``};``        ``int` `k = ``3``;``        ``int` `n = arr.length;` `        ``reverse(arr, n, k);``        ``for` `(``int` `i = ``0``; i < n; i++)``        ``{``            ``System.out.print(arr[i] + ``" "``);``        ``}``    ``}``}` `// This code has been contributed by 29AjayKumar`

## Python3

 `# Python3 program to reverse every alternate sub-array``# formed by consecutive k elements` `# Function to reverse every alternate sub-array``# formed by consecutive k elements``def` `reverse(arr, n, k):``    ``# increment i in multiples of 2*k``    ``for` `i ``in` `range``(``0``,n,``2``*``k):``        ``left ``=` `i` `        ``# to handle case when 2*k is not multiple of n``        ``right ``=` `min``(i ``+` `k ``-` `1``, n ``-` `1``)` `        ``# reverse the sub-array [left, right]``        ``while` `(left < right):``            ``temp ``=` `arr[left]``            ``arr[left] ``=` `arr[right]``            ``arr[right] ``=` `temp``            ``left ``+``=` `1``            ``right ``-``=` `1``            ` `# Driver code``if` `__name__ ``=``=` `'__main__'``:``    ``arr ``=` `[``1``, ``2``, ``3``, ``4``, ``5``, ``6``, ``7``, ``8``, ``9``, ``10``, ``11``, ``12``, ``13``, ``14``]``    ``k ``=` `3` `    ``n ``=` `len``(arr)` `    ``reverse(arr, n, k)` `    ``for` `i ``in` `range``(``0``,n,``1``):``        ``print``(arr[i],end ``=``" "``)``        ` `# This code is contributed by``# Surendra_Gangwar`

## C#

 `// C# program to reverse every alternate``// sub-array formed by consecutive k elements``using` `System;``    ` `class` `GFG``{` `    ``// Function to reverse every``    ``// alternate sub-array formed``    ``// by consecutive k elements``    ``static` `void` `reverse(``int` `[]arr,``                        ``int` `n, ``int` `k)``    ``{``        ` `        ``// increment i in multiples of 2*k``        ``for` `(``int` `i = 0; i < n; i += 2 * k)``        ``{``            ``int` `left = i;` `            ``// to handle case when 2*k is``            ``// not multiple of n``            ``int` `right = Math.Min(i + k - 1, n - 1);` `            ``// reverse the sub-array [left, right]``            ``while` `(left < right)``            ``{``                ``swap(arr, left++, right--);``            ``}``        ``}``    ``}` `    ``static` `int``[] swap(``int``[] array, ``int` `i, ``int` `j)``    ``{``        ``int` `temp = array[i];``        ``array[i] = array[j];``        ``array[j] = temp;``        ``return` `array;``    ``}` `    ``// Driver code``    ``public` `static` `void` `Main(String[] args)``    ``{``        ``int` `[]arr = {1, 2, 3, 4, 5, 6, 7, 8,``                     ``9, 10, 11, 12, 13, 14};``        ``int` `k = 3;``        ``int` `n = arr.Length;` `        ``reverse(arr, n, k);``        ``for` `(``int` `i = 0; i < n; i++)``        ``{``            ``Console.Write(arr[i] + ``" "``);``        ``}``    ``}``}` `// This code is ontributed by PrinciRaj1992`

## Javascript

 ``

Output:

`3 2 1 4 5 6 9 8 7 10 11 12 14 13`

Variation 2 (Reverse at given distance):
Reverse every sub-array formed by consecutive k elements at given distance apart.

Examples:

```Input:
arr = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
k = 3
m = 2
Output:
[3, 2, 1, 4, 5, 8, 7, 6, 9, 10]

Input:
arr = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
k = 3
m = 1
Output:
[3, 2, 1, 4, 7, 6, 5, 8, 10, 9]

Input:
arr = [1, 2, 3, 4, 5, 6, 7, 8]
k = 2
m = 0
Output:
[2, 1, 4, 3, 6, 5, 8, 7]```

Below is its implementation –

## C++

 `// C++ program to reverse every sub-array formed by``// consecutive k elements at given distance apart``#include ``using` `namespace` `std;` `// Function to reverse every sub-array formed by``// consecutive k elements at m distance apart``void` `reverse(``int` `arr[], ``int` `n, ``int` `k, ``int` `m)``{``    ``// increment i in multiples of k + m``    ``for` `(``int` `i = 0; i < n; i += k + m)``    ``{``        ``int` `left = i;` `        ``// to handle case when k + m is not multiple of n``        ``int` `right = min(i + k - 1, n - 1);` `        ``// reverse the sub-array [left, right]``        ``while` `(left < right)``            ``swap(arr[left++], arr[right--]);``    ``}``}` `// Driver code``int` `main()``{``    ``int` `arr[] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14};``    ``int` `k = 3;``    ``int` `m = 2;` `    ``int` `n = ``sizeof``(arr) / ``sizeof``(arr);` `    ``reverse(arr, n, k, m);` `    ``for` `(``int` `i = 0; i < n; i++)``        ``cout << arr[i] << ``" "``;` `    ``return` `0;``}`

## Java

 `// java program to reverse every sub-array formed by``// consecutive k elements at given distance apart``class` `GFG``{` `// Function to reverse every sub-array formed by``// consecutive k elements at m distance apart``static` `void` `reverse(``int``[] arr, ``int` `n, ``int` `k, ``int` `m)``{``    ``// increment i in multiples of k + m``    ``for` `(``int` `i = ``0``; i < n; i += k + m)``    ``{``        ``int` `left = i;` `        ``// to handle case when k + m is not multiple of n``        ``int` `right = Math.min(i + k - ``1``, n - ``1``);` `        ``// reverse the sub-array [left, right]``        ``while` `(left < right)``            ``swap(arr,left++, right--);``    ``}``}`` ``static` `int``[] swap(``int``[] arr, ``int` `i, ``int` `j)``    ``{``        ``int` `temp = arr[i];``        ``arr[i] = arr[j];``        ``arr[j] = temp;``        ``return` `arr;``    ``}` `// Driver code`` ``public` `static` `void` `main(String[] args)``    ``{``        ``int` `arr[] = {``1``, ``2``, ``3``, ``4``, ``5``, ``6``, ``7``, ``8``,``                    ``9``, ``10``, ``11``, ``12``, ``13``, ``14``};``        ``int` `k = ``3``;``        ``int` `m = ``2``;``        ``int` `n = arr.length;`` ` `        ``reverse(arr, n, k, m );``        ``for` `(``int` `i = ``0``; i < n; i++)``        ``{``            ``System.out.print(arr[i] + ``" "``);``        ``}``    ``}``}``// This code has been contributed by Rajput-Ji`

## Python3

 `# Python3 program to reverse every``# sub-array formed by consecutive``# k elements at given distance apart` `# Function to reverse every``# sub-array formed by consecutive``# k elements at m distance apart``def` `reverse(arr, n, k, m):``    ` `    ``# increment i in multiples of k + m``    ``for` `i ``in` `range``(``0``, n, k ``+` `m):``        ``left ``=` `i;` `        ``# to handle case when k + m``        ``# is not multiple of n``        ``right ``=` `min``(i ``+` `k ``-` `1``, n ``-` `1``);` `        ``# reverse the sub-array [left, right]``        ``while` `(left < right):``            ``arr ``=` `swap(arr,left, right);``            ``left ``+``=` `1``;``            ``right ``-``=` `1``;``    ``return` `arr;` `def` `swap(arr, i, j):` `    ``temp ``=` `arr[i];``    ``arr[i] ``=` `arr[j];``    ``arr[j] ``=` `temp;``    ``return` `arr;` `# Driver code``arr ``=` `[``1``, ``2``, ``3``, ``4``, ``5``, ``6``, ``7``,``       ``8``, ``9``, ``10``, ``11``, ``12``, ``13``, ``14``];``k ``=` `3``;``m ``=` `2``;``n ``=` `len``(arr);` `arr ``=` `reverse(arr, n, k, m );``for` `i ``in` `range``(``0``, n):``    ``print``(arr[i], end ``=` `" "``);``    ` `# This code is contributed by Rajput-Ji`

## C#

 `// C# program to reverse every sub-array``// formed by consecutive k elements at``// given distance apart``using` `System;``    ` `class` `GFG``{` `// Function to reverse every sub-array``// formed by consecutive k elements``// at m distance apart``static` `void` `reverse(``int``[] arr, ``int` `n,``                    ``int` `k, ``int` `m)``{``    ``// increment i in multiples of k + m``    ``for` `(``int` `i = 0; i < n; i += k + m)``    ``{``        ``int` `left = i;` `        ``// to handle case when k + m is``        ``// not multiple of n``        ``int` `right = Math.Min(i + k - 1, n - 1);` `        ``// reverse the sub-array [left, right]``        ``while` `(left < right)``            ``swap(arr, left++, right--);``    ``}``}` `static` `int``[] swap(``int``[] arr, ``int` `i, ``int` `j)``{``    ``int` `temp = arr[i];``    ``arr[i] = arr[j];``    ``arr[j] = temp;``    ``return` `arr;``}` `// Driver code``public` `static` `void` `Main(String[] args)``{``    ``int` `[]arr = {1, 2, 3, 4, 5, 6, 7, 8,``                 ``9, 10, 11, 12, 13, 14};``    ``int` `k = 3;``    ``int` `m = 2;``    ``int` `n = arr.Length;` `    ``reverse(arr, n, k, m );``    ``for` `(``int` `i = 0; i < n; i++)``    ``{``        ``Console.Write(arr[i] + ``" "``);``    ``}``}``}` `// This code is contributed by PrinciRaj1992`

## Javascript

 ``

Output:

`3 2 1 4 5 8 7 6 9 10 13 12 11 14`

Variation 3 (Reverse by doubling the group size):
Reverse every sub-array formed by consecutive k elements where k doubles itself with every sub-array.

Examples:

```Input:
arr = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15]
k = 1
Output:
, [3, 2], [7, 6, 5, 4], [15, 14, 13, 12, 11, 10, 9, 8]```

Below is its implementation –

## C++

 `// C++ program to reverse every sub-array formed by``// consecutive k elements where k doubles itself with``// every sub-array.``#include ``using` `namespace` `std;` `// Function to reverse every sub-array formed by``// consecutive k elements where k doubles itself``// with every sub-array.``void` `reverse(``int` `arr[], ``int` `n, ``int` `k)``{``    ``// increment i in multiples of k where value``    ``// of k is doubled with each iteration``    ``for` `(``int` `i = 0; i < n; i += k/2)``    ``{``        ``int` `left = i;` `        ``// to handle case when number of elements in``        ``// last group is less than k``        ``int` `right = min(i + k - 1, n - 1);` `        ``// reverse the sub-array [left, right]``        ``while` `(left < right)``            ``swap(arr[left++], arr[right--]);` `        ``// double value of k with each iteration``        ``k = k*2;``    ``}``}` `// Driver code``int` `main()``{``    ``int` `arr[] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16};``    ``int` `k = 1;` `    ``int` `n = ``sizeof``(arr) / ``sizeof``(arr);` `    ``reverse(arr, n, k);` `    ``for` `(``int` `i = 0; i < n; i++)``        ``cout << arr[i] << ``" "``;` `    ``return` `0;``}`

## Java

 `// Java program to reverse every sub-array``// formed by consecutive k elements where``// k doubles itself with every sub-array.``import` `java.util.*;` `class` `GFG``{` `// Function to reverse every sub-array formed by``// consecutive k elements where k doubles itself``// with every sub-array.``static` `void` `reverse(``int` `arr[], ``int` `n, ``int` `k)``{``    ``// increment i in multiples of k where value``    ``// of k is doubled with each iteration``    ``for` `(``int` `i = ``0``; i < n; i += k / ``2``)``    ``{``        ``int` `left = i;` `        ``// to handle case when number of elements in``        ``// last group is less than k``        ``int` `right = Math.min(i + k - ``1``, n - ``1``);` `        ``// reverse the sub-array [left, right]``        ``while` `(left < right)``            ``swap(arr, left++, right--);` `        ``// double value of k with each iteration``        ``k = k * ``2``;``    ``}``}` `static` `int``[] swap(``int``[] arr, ``int` `i, ``int` `j)``{``    ``int` `temp = arr[i];``    ``arr[i] = arr[j];``    ``arr[j] = temp;``    ``return` `arr;``}` `// Driver code``public` `static` `void` `main(String[] args)``{``    ``int` `arr[] = {``1``, ``2``, ``3``, ``4``, ``5``, ``6``, ``7``, ``8``, ``9``,``                ``10``, ``11``, ``12``, ``13``, ``14``, ``15``, ``16``};``    ``int` `k = ``1``;` `    ``int` `n = arr.length;` `    ``reverse(arr, n, k);` `    ``for` `(``int` `i = ``0``; i < n; i++)``        ``System.out.print(arr[i] + ``" "``);``}``}` `// This code is contributed by 29AjayKumar`

## Python3

 `# Python3 program to reverse every``# sub-array formed by consecutive``# k elements where k doubles itself``# with every sub-array` `# Function to reverse every sub-array``# formed by consecutive k elements``# where k doubles itself with every``# sub-array``def` `reverse(arr, n, k):``    ` `    ``i ``=` `0` `    ``# Increment i in multiples of k where``    ``# value of k is doubled with each``    ``# iteration``    ``while` `(i < n):``        ``left ``=` `i` `        ``# To handle case when number of elements``        ``# in last group is less than k``        ``right ``=` `min``(i ``+` `k ``-` `1``, n ``-` `1``)` `        ``# Reverse the sub-array [left, right]``        ``while` `(left < right):``            ``arr[left], arr[right] ``=` `arr[right], arr[left]``            ``left ``+``=` `1``            ``right ``-``=` `1``            ` `        ``# Double value of k with each iteration``        ``k ``=` `k ``*` `2``        ``i ``+``=` `int``(k ``/` `2``)` `# Driver code``arr ``=` `[ ``1``, ``2``, ``3``, ``4``, ``5``, ``6``, ``7``, ``8``, ``9``,``        ``10``, ``11``, ``12``, ``13``, ``14``, ``15``, ``16``]``k ``=` `1` `n ``=` `len``(arr)` `reverse(arr, n, k)` `print``(``*``arr, sep ``=` `' '``)` `# This code is contributed by avanitrachhadiya2155`

## C#

 `// C# program to reverse every sub-array``// formed by consecutive k elements where``// k doubles itself with every sub-array.``using` `System;``    ` `class` `GFG``{` `// Function to reverse every sub-array formed by``// consecutive k elements where k doubles itself``// with every sub-array.``static` `void` `reverse(``int` `[]arr, ``int` `n, ``int` `k)``{``    ``// increment i in multiples of k where value``    ``// of k is doubled with each iteration``    ``for` `(``int` `i = 0; i < n; i += k / 2)``    ``{``        ``int` `left = i;` `        ``// to handle case when number of elements in``        ``// last group is less than k``        ``int` `right = Math.Min(i + k - 1, n - 1);` `        ``// reverse the sub-array [left, right]``        ``while` `(left < right)``            ``swap(arr, left++, right--);` `        ``// double value of k with each iteration``        ``k = k * 2;``    ``}``}` `static` `int``[] swap(``int``[] arr, ``int` `i, ``int` `j)``{``    ``int` `temp = arr[i];``    ``arr[i] = arr[j];``    ``arr[j] = temp;``    ``return` `arr;``}` `// Driver code``public` `static` `void` `Main(String[] args)``{``    ``int` `[]arr = {1, 2, 3, 4, 5, 6, 7, 8, 9,``                ``10, 11, 12, 13, 14, 15, 16};``    ``int` `k = 1;` `    ``int` `n = arr.Length;` `    ``reverse(arr, n, k);` `    ``for` `(``int` `i = 0; i < n; i++)``        ``Console.Write(arr[i] + ``" "``);``}``}` `// This code is contributed by Rajput-Ji`

## Javascript

 ``

Output:

`1 3 2 7 6 5 4 15 14 13 12 11 10 9 8 16`

Time complexity of all solutions discussed above is O(n).
Auxiliary space used by the program is O(1).