# Write a program to reverse an array or string

We are given an array (or string), the task is to reverse the array.

Examples:

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

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

## Recommended: Please solve it on “PRACTICE ” first, before moving on to the solution.

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

Another example to reverse a string:

## C

```// Iterative C program to reverse an array
#include<stdio.h>

/* 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};
printArray(arr, 6);
rvereseArray(arr, 0, 5);
printf("Reversed array is \n");
printArray(arr, 6);
return 0;
}
```

## Java

```// Java program to reverse an array
import java.io.*;

class ReverseArray {

/* Function to reverse arr[] from start to end*/
static 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 */
static void printArray(int arr[], int size)
{
int i;
for (i=0; i < size; i++)
System.out.print(arr[i] + " ");
System.out.println("");
}

/*Driver function to check for above functions*/
public static void main (String[] args) {
int arr[] = {1, 2, 3, 4, 5, 6};
printArray(arr, 6);
rvereseArray(arr, 0, 5);
System.out.println("Reversed array is ");
printArray(arr, 6);
}
}
/*This code is contributed by Devesh Agrawal*/
```

## Python

```# Iterative python program to reverse an array

# Function to reverse A[] from start to end
def reverseList(A, start, end):
while start < end:
A[start], A[end] = A[end], A[start]
start += 1
end -= 1

# Driver function to test above function
A = [1, 2, 3, 4, 5, 6]
print(A)
reverseList(A, 0, 5)
print("Reversed list is")
print(A)
# This program is contributed by Pratik Chhajer
```

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

## C

```// Recursive C program to reverse an array
#include <stdio.h>

/* 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;
}
```

## Java

```// Recursive Java Program to reverse an array
import java.io.*;

class ReverseArray {

/* Function to reverse arr[] from start to end*/
static 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 */
static void printArray(int arr[], int size)
{
for (int i=0; i < size; i++)
System.out.print(arr[i] + " ");
System.out.println("");
}

/*Driver function to check for above functions*/
public static void main (String[] args) {
int arr[] = {1, 2, 3, 4, 5, 6};
printArray(arr, 6);
rvereseArray(arr, 0, 5);
System.out.println("Reversed array is ");
printArray(arr, 6);
}
}
```

## Python

```# Recursive python program to reverse an array

# Function to reverse A[] from start to end
def reverseList(A, start, end):
if start >= end:
return
A[start], A[end] = A[end], A[start]
reverseList(A, start+1, end-1)

# Driver function to test above function
A = [1, 2, 3, 4, 5, 6]
print(A)
reverseList(A, 0, 5)
print("Reversed list is")
print(A)
# This program is contributed by Pratik Chhajer
```

Output:
```1 2 3 4 5 6
Reversed array is
6 5 4 3 2 1 ```

Time Complexity: O(n)

Please write comments if you find any bug in the above programs or other ways to solve the same problem.

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