Write a program to reverse an array or string

• Difficulty Level : Basic
• Last Updated : 08 Sep, 2020

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}

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

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 : 
 

• C++
• C
• Java
• Python
• C#
• PHP

// 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 6Reversed array is6 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 : 
 

• C++
• C
• Java
• Python
• C#
• PHP

// 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 6Reversed array is6 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]