ritisha8/recursion_cpp

reversing an array using recursion in c++

Recursion CPP:

Reversing an array using recursion in c++

This is a functional recursive code for reversing an array in C++. Recursion is used when we want a function to return a value or perform a repeated task. This type of recursion is commonly used in dynamic programming.

Two Pointers Approach to Reverse an Array

The two-pointers approach is an efficient way to reverse an array by utilizing two indices that start from the opposite ends of the array and move towards the center. This method is simple and works in-place, meaning it requires no extra space apart from the input array.

Explanation

Consider an array: [1, 2, 3, 4, 5].

We use two pointers:

• start pointer, which starts at the beginning of the array.
• end pointer, which starts at the end of the array.

The idea is to swap the elements at the start and end pointers and then move these pointers towards the center. This process is repeated until the start pointer is no longer less than the end pointer.

Step-by-Step Example

Initial array:

1	2	3	4	5
⬆				⬆
start				end

1. Swap arr[start] and arr[end]:

5	2	3	4	1
⬆				⬆
start				end

2. Move start pointer to the right and end pointer to the left:

5	2	3	4	1
	⬆		⬆
	start		end

3. Swap arr[start] and arr[end]:

5	4	3	2	1
	⬆		⬆
	start		end

4. Move start pointer to the right and end pointer to the left:

5	4	3	2	1
		⬆
		start, end

5. Now, start is no longer less than end, so the process stops.

Recursive Implementation

Here's a C++ implementation of this approach using recursion:

void reverseArr(int arr[], int start, int end){
    if(start < end){
        swap(arr[start], arr[end]);
        reverseArr(arr, start+1, end-1);
    }
    else return;
}

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