# Generating subarrays using recursion

Hello Everyone,

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]

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++ code to print all possible subarrays

// for given array using recursion

#include <iostream>

# include <vector>

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;

}

Output:

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

Time Complexity: O(n^2)