Hello Everyone,
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 :
- Initialize start and end indexes as start = 0, end = n-1
- In a loop, swap arr[start] with arr[end] and change start and end as follows :
start = start +1, end = end – 1
Below is the implementation of the above approach :
- C++
// Iterative C++ program to reverse an array
#include <bits/stdc++.h>
using
namespace
std;
/* Function to reverse arr[] from start to end*/
void
rvereseArray(
int
arr[],
int
start,
int
end)
{
while
(start < end)
{
int
temp = arr[start];
arr[start] = arr[end];
arr[end] = temp;
start++;
end--;
}
}
/* Utility function to print an array */
void
printArray(
int
arr[],
int
size)
{
for
(
int
i = 0; i < size; i++)
cout << arr[i] <<
" "
;
cout << endl;
}
/* Driver function to test above functions */
int
main()
{
int
arr[] = {1, 2, 3, 4, 5, 6};
int
n =
sizeof
(arr) /
sizeof
(arr[0]);
// To print original array
printArray(arr, n);
// Function calling
rvereseArray(arr, 0, n-1);
cout <<
"Reversed array is"
<< endl;
// To print the Reversed array
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 :
- Initialize start and end indexes as start = 0, end = n-1
- Swap arr[start] with arr[end]
- Recursively call reverse for rest of the array.
Below is the implementation of the above approach :
- C++
// Recursive C++ program to reverse an array
#include <bits/stdc++.h>
using
namespace
std;
/* Function to reverse arr[] from start to end*/
void
rvereseArray(
int
arr[],
int
start,
int
end)
{
if
(start >= end)
return
;
int
temp = arr[start];
arr[start] = arr[end];
arr[end] = temp;
// Recursive Function calling
rvereseArray(arr, start + 1, end - 1);
}
/* Utility function to print an array */
void
printArray(
int
arr[],
int
size)
{
for
(
int
i = 0; i < size; i++)
cout << arr[i] <<
" "
;
cout << endl;
}
/* Driver function to test above functions */
int
main()
{
int
arr[] = {1, 2, 3, 4, 5, 6};
// To print original array
printArray(arr, 6);
// Function calling
rvereseArray(arr, 0, 5);
cout <<
"Reversed array is"
<< endl;
// To print the Reversed array
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
- Python3
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]
Please write comments if you find any bug in the above programs or other ways to solve the same problem.