Write a program to reverse an array or string

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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

reverse-a-number

Another example to reverse a string:

reverse-a-string

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; 
} 

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}; 
    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; 
} 

Java

// Iterative java program to reverse an 
// array 
public class GFG { 
      
   /* Function to reverse arr[] from  
    start to end*/
    static 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 */
    static void printArray(int arr[],  
                            int size) 
    { 
        for (int i = 0; i < size; i++) 
             System.out.print(arr[i] + " "); 
           
         System.out.println(); 
    }  
  
    // Driver code 
    public static void main(String args[]) { 
          
        int arr[] = {1, 2, 3, 4, 5, 6}; 
        printArray(arr, 6); 
        rvereseArray(arr, 0, 5); 
        System.out.print("Reversed array is \n"); 
        printArray(arr, 6);  
         
    } 
} 
  
// This code is contributed by Sam007 

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 

C#

// Iterative C# program to reverse an 
// array 
using System; 
  
class GFG { 
  
    /* Function to reverse arr[] from  
    start to end*/
    static 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 */
    static void printArray(int []arr,  
                            int size) 
    { 
        for (int i = 0; i < size; i++) 
            Console.Write(arr[i] + " "); 
          
        Console.WriteLine(); 
    }  
      
    // Driver function 
    public static void Main() 
    { 
        int []arr = {1, 2, 3, 4, 5, 6}; 
        printArray(arr, 6); 
        rvereseArray(arr, 0, 5); 
        Console.Write("Reversed array is \n"); 
        printArray(arr, 6);  
    } 
} 
  
// This code is contributed by Sam007 

PHP

<?php  
// Iterative PHP program  
// to reverse an array 
  
/* Function to reverse  
$arr from start to end*/
function rvereseArray(&$arr, $start,  
                       $end) 
{ 
    while ($start < $end) 
    { 
        $temp = $arr[$start];  
        $arr[$start] = $arr[$end]; 
        $arr[$end] = $temp; 
        $start++; 
        $end--; 
    }  
}      
  
/* Utility function to  
   print an array */
function printArray(&$arr, $size) 
{ 
for ($i = 0; $i < $size; $i++) 
echo $arr[$i] . " "; 
  
echo "\n"; 
}  
  
// Driver code 
$arr = array(1, 2, 3, 4, 5, 6); 
  
// To print original array 
printArray($arr, 6); 
  
// Function calling 
rvereseArray($arr, 0, 5); 
  
echo "Reversed array is" ."\n"; 
  
// To print the Reversed array 
printArray($arr, 6); 
  
// This code is contributed 
// by ChitraNayal 
?> 

javascript

// Iterative Javascript program to reverse an array 
  
/* Function to reverse arr[] from start to end*/
function rvereseArray(arr,start,end) 
{ 
    while (start < end) 
    {    
        var temp = arr[start]; 
        arr[start] = arr[end]; 
        arr[end] = temp; 
        start++; 
        end--; 
    } 
}     
   
/* Utility function to print an array */
function printArray(arr,size) 
{ 
   for (var i = 0; i < size; i++){ 
   console.log(arr[i]); 
   } 
} 
   
/* Driver function to test above functions */
    var arr= [1, 2, 3, 4, 5, 6]; 
    var n = 6; 
    // To print original array 
    printArray(arr, n); 
       
    // Function calling 
    rvereseArray(arr, 0, n-1); 
       
    console.log("Reversed array is");  
       
    // To print the Reversed array 
    printArray(arr, n); 

Output :

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

Time Complexity: O(n)
Auxiliary Space: O(1)
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++

// 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; 
} 

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, 6}; 
    printArray(arr, 6); 
    rvereseArray(arr, 0, 5); 
    printf("Reversed array is \n"); 
    printArray(arr, 6);     
    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); 
    } 
} 
/*This article is contributed by Devesh Agrawal*/

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 

C#

// C# program to reverse an array 
using System; 
  
class GFG 
{ 
    /* 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++) 
            Console.Write(arr[i] + " "); 
      
        Console.WriteLine(""); 
    } 
  
    // Driver Code 
    public static void Main ()  
    { 
        int []arr = {1, 2, 3, 4, 5, 6}; 
          
        printArray(arr, 6); 
        rvereseArray(arr, 0, 5); 
          
        Console.WriteLine("Reversed array is "); 
        printArray(arr, 6); 
    } 
} 
  
// This code is contributed by Sam007 

PHP

<?php  
// Iterative PHP program  
// to reverse an array 
  
/* Function to reverse 
$arr from start to end*/
function rvereseArray(&$arr,  
                       $start, $end) 
{ 
    if ($start >= $end) 
    return; 
      
    $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 */
function printArray(&$arr, $size) 
{ 
for ($i = 0; $i < $size; $i++) 
echo $arr[$i] . " "; 
  
echo "\n"; 
}  
  
// Driver code 
$arr = array(1, 2, 3, 4, 5, 6); 
  
// To print original array 
printArray($arr, 6); 
  
// Function calling 
rvereseArray($arr, 0, 5); 
  
echo "Reversed array is" ."\n"; 
  
// To print the Reversed array 
printArray($arr, 6); 
  
// This code is contributed 
// by ChitraNayal 
?> 

javascript

// Recursive Javascript program to reverse an array 
  
/* Function to reverse arr[] from start to end*/
function rvereseArray(arr,start,end) 
{ 
    var temp = arr[start]; 
    arr[start] = arr[end]; 
    arr[end] = temp; 
      
// Recursive Function calling 
    if (start+1<end-1){ 
    rvereseArray(arr, start + 1, end - 1); 
    } 
}     
/* Utility function to print an array */
function printArray(arr,size) 
{ 
for (var i = 0; i < size; i++){ 
console.log(arr[i]); 
  } 
} 
  
/* Driver function to test above functions */
  
    var arr= [1, 2, 3, 4, 5, 6]; 
      
    // To print original array 
    printArray(arr, 6); 
      
    // Function calling 
    rvereseArray(arr, 0, 5); 
      
    console.log("Reversed array is");  
      
    // To print the Reversed array 
    printArray(arr, 6); 

Output :

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

Time Complexity: O(n)
Auxiliary Space: 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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Last Updated : 06 Oct, 2023