Given an array (or string), the task is to reverse the array/string.
Examples : 

Input  : arr[] = {1, 2, 3}
Output : arr[] = {3, 2, 1}

Input :  arr[] = {4, 5, 1, 2}
Output : arr[] = {2, 1, 5, 4}

Iterative way 

      1) Initialize start and end indexes as start = 0, end = n-1 
      2) In a loop, swap arr[start] with arr[end] and change start and end as follows : 
      start = start +1, end = end – 1

Another example to reverse a string:

Below is the implementation of the above approach : 

// Iterative C program to reverse an array
#include

/* Function to reverse arr[] from start to end*/
void rvereseArray(int arr[], int start, int end)
{
	int temp;
	while (start < end)
	{
		temp = arr[start];
		arr[start] = arr[end];
		arr[end] = temp;
		start++;
		end--;
	}
}	

/* Utility that prints out an array on a line */
void printArray(int arr[], int size)
{
int i;
for (i=0; i < size; i++)
	printf("%d ", arr[i]);

printf("\n");
}

/* Driver function to test above functions */
int main()
{
	int arr[] = {1, 2, 3, 4, 5, 6};
	int n = sizeof(arr) / sizeof(arr[0]);
	printArray(arr, n);
	rvereseArray(arr, 0, n-1);
	printf("Reversed array is \n");
	printArray(arr, n);
	return 0;
}

Output : 

1 2 3 4 5 6 
Reversed array is 
6 5 4 3 2 1 

Time Complexity : O(n)
Recursive Way :
 

1) Initialize start and end indexes as start = 0, end = n-1 
2) Swap arr[start] with arr[end] 
3) Recursively call reverse for rest of the array.

Below is the implementation of the above approach : 

// Recursive C program to reverse an array
#include 

/* Function to reverse arr[] from start to end*/
void rvereseArray(int arr[], int start, int end)
{
int temp;
if (start >= end)
	return;
temp = arr[start];
arr[start] = arr[end];
arr[end] = temp;
rvereseArray(arr, start+1, end-1);
}	

/* Utility that prints out an array on a line */
void printArray(int arr[], int size)
{
int i;
for (i=0; i < size; i++)
	printf("%d ", arr[i]);

printf("\n");
}

/* Driver function to test above functions */
int main()
{
	int arr[] = {1, 2, 3, 4, 5, 6};
	printArray(arr, 6);
	rvereseArray(arr, 0, 5);
	printf("Reversed array is \n");
	printArray(arr, 6);
	return 0;
}

Output : 

1 2 3 4 5 6 
Reversed array is 
6 5 4 3 2 1 

Time Complexity : O(n)

Another Approach: Using Python List slicing

def reverseList(A):
print( A[::-1])
	
# Driver function to test above function
A = [1, 2, 3, 4, 5, 6]
print(A)
print("Reversed list is")
reverseList(A)

Output:

[1, 2, 3, 4, 5, 6]
Reversed list is
[6, 5, 4, 3, 2, 1]