🔥 ข่าวด่วน: web//https://www.geeksforgeeks.org/write a program to reverse an array or string

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
?>

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 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
?>

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.

Attention reader! Don’t stop learning now. Get hold of all the important DSA concepts with the DSA Self Paced Course at a student-friendly price and become industry ready.

My Personal Notes

Oct	NOV	Dec
	02
2019	2020	2021

Write a program to reverse an array or string

C++

C

Java

Python

C#

PHP

C++

C

Java

Python

C#

PHP

Python3

Recommended Posts: