# Generating subarrays using recursion

Given an array, generate all the possible subarrays of the given array using recursion.

Examples:

```Input : [1, 2, 3]
Output : [1], [1, 2], [2], [1, 2, 3], [2, 3], [3]

Input : [1, 2]
Output : [1], [1, 2], [2]```

We have discussed iterative program to generate all subarrays. In this post, recursive is discussed.

Approach: We use two pointers start and end to maintain the starting and ending point of the array and follow the steps given below:

• Stop if we have reached the end of the array
• Increment the end index if start has become greater than end
• Print the subarray from index start to end and increment the starting index

Below is the implementation of the above approach.

## C++

 `// C++ code to print all possible subarrays for given array` `// using recursion`   `#include ` `using` `namespace` `std;`   `// Recursive function to print all possible subarrays for` `// given array` `void` `printSubArrays(vector<``int``> arr, ``int` `start, ``int` `end)` `{` `    ``// Stop if we have reached the end of the array` `    ``if` `(end == arr.size())` `        ``return``;` `    ``// Increment the end point and start from 0` `    ``else` `if` `(start > end)` `        ``printSubArrays(arr, 0, end + 1);` `    ``// Print the subarray and increment the starting point` `    ``else` `{` `        ``cout << ``"["``;` `        ``for` `(``int` `i = start; i < end; i++)` `            ``cout << arr[i] << ``", "``;` `        ``cout << arr[end] << ``"]"` `<< endl;` `        ``printSubArrays(arr, start + 1, end);` `    ``}` `    ``return``;` `}`   `int` `main()` `{` `    ``vector<``int``> arr = { 1, 2, 3 };` `    ``printSubArrays(arr, 0, 0);` `    ``return` `0;` `}`   `// This code is contributed by Sania Kumari Gupta`

## C

 `// C code to print all possible subarrays for given array` `// using recursion` `#include `   `// Recursive function to print all possible subarrays for` `// given array` `void` `printSubArrays(``int` `arr[], ``int` `start, ``int` `end, ``int` `size)` `{` `  `  `    ``// Stop if we have reached the end of the array` `    ``if` `(end == size)` `        ``return``;` `  `  `    ``// Increment the end point and start from 0` `    ``else` `if` `(start > end)` `        ``printSubArrays(arr, 0, end + 1, size);` `  `  `    ``// Print the subarray and increment the starting point` `    ``else` `{` `        ``printf``(``"["``);` `        ``for` `(``int` `i = start; i < end; i++)` `            ``printf``(``"%d, "``, arr[i]);` `      `  `        ``// cout << arr[i] << ", ";` `        ``printf``(``"%d]\n"``, arr[end]);` `      `  `        ``// cout << arr[end] << "]" << endl;` `        ``printSubArrays(arr, start + 1, end, size);` `    ``}` `    ``return``;` `}`   `int` `main()` `{` `    ``int` `arr[] = { 1, 2, 3 };` `    ``int` `n = ``sizeof``(arr) / ``sizeof``(arr[0]);` `    ``printSubArrays(arr, 0, 0, n);` `    ``return` `0;` `}`   `// This code is contributed by Sania Kumari Gupta`

## Java

 `// Java code to print all possible subarrays for given array` `// using recursion`   `class` `solution {`   `    ``// Recursive function to print all possible subarrays` `    ``// for given array` `    ``static` `void` `printSubArrays(``int``[] arr, ``int` `start, ``int` `end)` `    ``{ ` `        ``// Stop if we have reached the end of the array` `        ``if` `(end == arr.length)` `            ``return``;` `        ``// Increment the end point and start from 0` `        ``else` `if` `(start > end)` `            ``printSubArrays(arr, ``0``, end + ``1``);` `        ``// Print the subarray and increment the starting` `        ``// point` `        ``else` `{` `            ``System.out.print(``"["``);` `            ``for` `(``int` `i = start; i < end; i++)` `                ``System.out.print(arr[i] + ``", "``);` `            ``System.out.println(arr[end] + ``"]"``);` `            ``printSubArrays(arr, start + ``1``, end);` `        ``}` `        ``return``;` `    ``}`   `    ``public` `static` `void` `main(String args[])` `    ``{` `        ``int``[] arr = { ``1``, ``2``, ``3` `};` `        ``printSubArrays(arr, ``0``, ``0``);` `    ``}` `}`   `// This code is contributed by Sania Kumari Gupta`

## Python3

 `# Python3 code to print all possible subarrays ` `# for given array using recursion`   `# Recursive function to print all possible subarrays ` `# for given array` `def` `printSubArrays(arr, start, end):` `    `  `    ``# Stop if we have reached the end of the array    ` `    ``if` `end ``=``=` `len``(arr):` `        ``return` `    `  `    ``# Increment the end point and start from 0` `    ``elif` `start > end:` `        ``return` `printSubArrays(arr, ``0``, end ``+` `1``)` `        `  `    ``# Print the subarray and increment the starting` `    ``# point` `    ``else``:` `        ``print``(arr[start:end ``+` `1``])` `        ``return` `printSubArrays(arr, start ``+` `1``, end)` `        `  `# Driver code` `arr ``=` `[``1``, ``2``, ``3``]` `printSubArrays(arr, ``0``, ``0``)`

## C#

 `// C# code to print all possible subarrays ` `// for given array using recursion ` `using` `System;`   `class` `GFG ` `{ `   `    ``// Recursive function to print all  ` `    ``// possible subarrays for given array ` `    ``static` `void` `printSubArrays(``int` `[]arr, ` `                        ``int` `start, ``int` `end) ` `    ``{ ` `        ``// Stop if we have reached ` `        ``// the end of the array ` `        ``if` `(end == arr.Length) ` `            ``return``; `   `        ``// Increment the end point ` `        ``// and start from 0 ` `        ``else` `if` `(start > end) ` `            ``printSubArrays(arr, 0, end + 1); `   `        ``// Print the subarray and ` `        ``// increment the starting point ` `        ``else` `        ``{ ` `            ``Console.Write(``"["``); ` `            ``for` `(``int` `i = start; i < end; i++)` `            ``{ ` `                ``Console.Write(arr[i]+``", "``); ` `            ``} `   `            ``Console.WriteLine(arr[end]+``"]"``); ` `            ``printSubArrays(arr, start + 1, end); ` `        ``} ` `        ``return``; ` `    ``} `   `    ``// Driver code` `    ``public` `static` `void` `Main(String []args) ` `    ``{ ` `        ``int` `[]arr = {1, 2, 3}; ` `        ``printSubArrays(arr, 0, 0); ` `    ``} ` `} `   `// This code is contributed by Rajput-Ji`

## PHP

 ` ``\$end``)` `        ``return` `printSubArrays(``\$arr``, 0, ` `                              ``\$end` `+ 1);` `        `  `    ``// Print the subarray and increment ` `    ``// the starting point` `    ``else` `    ``{` `    ``echo` `"["``;` `    ``for``(``\$i` `= ``\$start``; ``\$i` `< ``\$end` `+ 1; ``\$i``++)` `    ``{` `        ``echo` `\$arr``[``\$i``];` `        ``if``(``\$i` `!= ``\$end``)` `        ``echo` `", "``;` `    ``}` `    ``echo` `"]\n"``;` `        ``return` `printSubArrays(``\$arr``, ``\$start` `+ 1, ` `                                    ``\$end``);` `    ``}` `} `   `// Driver code` `\$arr` `= ``array``(1, 2, 3);` `printSubArrays(``\$arr``, 0, 0);`   `// This code is contributed by mits` `?>`

## Javascript

 ``

Output:

```[1]
[1, 2]
[2]
[1, 2, 3]
[2, 3]
[3]```

Time Complexity: O(2n)

Auxiliary Space: O(2n)

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