Home Arrays Write a program to reverse an array.

# Write a program to reverse an array.

Iterative way:
1) Initialize start and end indexes.
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

/* 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(void)
{
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;
}


Time Complexity: O(n)

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

/* 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};
printArray(arr, 5);
rvereseArray(arr, 0, 4);
printf("Reversed array is \n");
printArray(arr, 5);
return 0;
}


Time Complexity: O(n)

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