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++
#include <bits/stdc++.h>
using namespace std;
void printSubArrays(vector<int> arr, int start, int end)
{
if (end == arr.size())
return;
else if (start > end)
printSubArrays(arr, 0, end + 1);
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;
}
|
C
#include <stdio.h>
void printSubArrays(int arr[], int start, int end, int size)
{
if (end == size)
return;
else if (start > end)
printSubArrays(arr, 0, end + 1, size);
else {
printf("[");
for (int i = start; i < end; i++)
printf("%d, ", arr[i]);
printf("%d]\n", arr[end]);
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;
}
|
Java
class solution {
static void printSubArrays(int[] arr, int start, int end)
{
if (end == arr.length)
return;
else if (start > end)
printSubArrays(arr, 0, end + 1);
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);
}
}
|
Python3
def printSubArrays(arr, start, end):
if end == len(arr):
return
elif start > end:
return printSubArrays(arr, 0, end + 1)
else:
print(arr[start:end + 1])
return printSubArrays(arr, start + 1, end)
arr = [1, 2, 3]
printSubArrays(arr, 0, 0)
|
C#
using System;
class GFG
{
static void printSubArrays(int []arr,
int start, int end)
{
if (end == arr.Length)
return;
else if (start > end)
printSubArrays(arr, 0, end + 1);
else
{
Console.Write("[");
for (int i = start; i < end; i++)
{
Console.Write(arr[i]+", ");
}
Console.WriteLine(arr[end]+"]");
printSubArrays(arr, start + 1, end);
}
return;
}
public static void Main(String []args)
{
int []arr = {1, 2, 3};
printSubArrays(arr, 0, 0);
}
}
|
PHP
<?php
function printSubArrays($arr, $start, $end)
{
if ($end == count($arr))
return;
else if ($start > $end)
return printSubArrays($arr, 0,
$end + 1);
else
{
echo "[";
for($i = $start; $i < $end + 1; $i++)
{
echo $arr[$i];
if($i != $end)
echo ", ";
}
echo "]\n";
return printSubArrays($arr, $start + 1,
$end);
}
}
$arr = array(1, 2, 3);
printSubArrays($arr, 0, 0);
?>
|
Javascript
<script>
function printSubArrays(arr, start, end)
{
if (end == arr.length)
return;
else if (start > end)
printSubArrays(arr, 0, end + 1);
else
{
document.write("[");
for(var i = start; i < end; i++)
{
document.write( arr[i] + ", ");
}
document.write(arr[end] + "]<br>");
printSubArrays(arr, start + 1, end);
}
return;
}
var arr = [ 1, 2, 3 ];
printSubArrays(arr, 0, 0);
</script>
|
Output:
[1]
[1, 2]
[2]
[1, 2, 3]
[2, 3]
[3]
Time Complexity: O(2n)
Auxiliary Space: O(2n)
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