How to Print a Reverse Array in C: In-Place vs. Extra Array Methods

When dealing with arrays, it's not uncommon to need to print a reverse array. Whether you prefer using an additional array or an in-place method, this guide will help you understand and implement both approaches effectively.

Understanding the Problem and the Terms

The given problem statement requires you to reverse an array but do it in-place. In-place, means that the approach should use the available space only, without the use of additional memory. This is in contrast to using an extra array, which can significantly increase the space complexity.

First Method: Not In-Place/By Using an Extra Array

This method involves creating a new array to store the reversed content. Here’s a step-by-step explanation:

Define the size of the original array and allocate memory accordingly. Initialize another array of the same size to store the reversed elements. Traverse the original array from the last index to the first, copying each element to the new array. Print the elements of the new array in order.

Here is the C code implementation:

#include using namespace std; int main() { cout Enter the size of the array: ; int n; cin n; int arr[n]; int reverseArr[n]; cout Enter the elements of the array: ; for(int i 0; i 0; i--) { reverseArr[j] arr[i]; j ; } cout The reversed array is: ; for(int i 0; i

Time Complexity: O(n)
Space Complexity: O(n)

Second Method: In-Place/Without Using an Extra Array

In this method, the original array is reversed in place, using only the available space. The approach involves swapping elements from both ends of the array, increasing the start pointer and decreasing the end pointer until they meet.

Here's how it works:

Define the size and elements of the original array. Use two pointers: one at the beginning and one at the end of the array. Swap the elements pointed to by the two pointers and adjust their positions.

Here is the C code implementation:

#include using namespace std; int main() { cout Enter the size of the array: ; int n; cin n; int arr[n]; cout Enter the elements of the array: ; for(int i 0; i

Time Complexity: O(n)
Space Complexity: O(1)

Conclusion and Final Thoughts

Both methods for printing a reverse array in C are useful, depending on your specific needs. The first method uses additional space but clarifies the operations. The second method, in-place reversal, is more memory-efficient and can be preferred for larger arrays or in environments with limited memory.

Understanding these techniques will help you manipulate arrays effectively and efficiently in C, whether you prefer clarity over resource usage or the other way around.