Array Reverse – Complete Tutorial
Last Updated :
25 Sep, 2024
Improve
Try it on GfG Practice 
Given an array arr[], the task is to reverse the array. Reversing an array means rearranging the elements such that the first element becomes the last, the second element becomes second last and so on.
Examples:
Input: arr[] = {1, 4, 3, 2, 6, 5}
Output: {5, 6, 2, 3, 4, 1}
Explanation: The first element 1 moves to last position, the second element 4 moves to second-last and so on.Input: arr[] = {4, 5, 1, 2}
Output: {2, 1, 5, 4}
Explanation: The first element 4 moves to last position, the second element 5 moves to second last and so on.
Table of Content
- [Naive Approach] Using a temporary array – O(n) Time and O(n) Space
- [Expected Approach – 1] Using Two Pointers – O(n) Time and O(1) Space
- [Expected Approach – 2] By Swapping Elements – O(n) Time and O(1) Space
- [Alternate Approach] Using Recursion – O(n) Time and O(n) Space
- Using Inbuilt Methods – O(n) Time and O(1) Space
[Naive Approach] Using a temporary array – O(n) Time and O(n) Space
The idea is to use a temporary array to store the reverse of the array.
- Create a temporary array of same size as the original array.
- Now, copy all elements from original array to the temporary array in reverse order.
- Finally, copy all the elements from temporary array back to the original array.
Working:
Below is the implementation of the algorithm:
// C++ Program to reverse an array using temporary array
#include <iostream>
#include <vector>
using namespace std;
// function to reverse an array
void reverseArray(vector<int> &arr) {
int n = arr.size();
// Temporary array to store elements in reversed order
vector<int> temp(n);
// Copy elements from original array to temp in reverse order
for(int i = 0; i < n; i++)
temp[i] = arr[n - i - 1];
// Copy elements back to original array
for(int i = 0; i < n; i++)
arr[i] = temp[i];
}
int main() {
vector<int> arr = { 1, 4, 3, 2, 6, 5 };
reverseArray(arr);
for(int i = 0; i < arr.size(); i++)
cout << arr[i] << " ";
return 0;
}
// C Program to reverse an array using temporary array
#include <stdio.h>
#include <stdlib.h>
// function to reverse an array
void reverseArray(int arr[], int n) {
// Temporary array to store elements in reversed order
int temp[n];
// Copy elements from original array to temp in reverse order
for(int i = 0; i < n; i++)
temp[i] = arr[n - i - 1];
// Copy elements back to original array
for(int i = 0; i < n; i++)
arr[i] = temp[i];
}
int main() {
int arr[] = { 1, 4, 3, 2, 6, 5 };
int n = sizeof(arr) / sizeof(arr[0]);
reverseArray(arr, n);
for(int i = 0; i < n; i++)
printf("%d ", arr[i]);
return 0;
}
// Java Program to reverse an array using temporary array
import java.util.Arrays;
class GfG {
// function to reverse an array
static void reverseArray(int[] arr) {
int n = arr.length;
// Temporary array to store elements in reversed order
int[] temp = new int[n];
// Copy elements from original array to temp in reverse order
for (int i = 0; i < n; i++)
temp[i] = arr[n - i - 1];
// Copy elements back to original array
for (int i = 0; i < n; i++)
arr[i] = temp[i];
}
public static void main(String[] args) {
int[] arr = { 1, 4, 3, 2, 6, 5 };
reverseArray(arr);
for (int i = 0; i < arr.length; i++)
System.out.print(arr[i] + " ");
}
}
# Python Program to reverse an array using temporary array
# function to reverse an array
def reverseArray(arr):
n = len(arr)
# Temporary array to store elements in reversed order
temp = [0] * n
# Copy elements from original array to temp in reverse order
for i in range(n):
temp[i] = arr[n - i - 1]
# Copy elements back to original array
for i in range(n):
arr[i] = temp[i]
if __name__ == "__main__":
arr = [1, 4, 3, 2, 6, 5]
reverseArray(arr)
for i in range(len(arr)):
print(arr[i], end=" ")
// C# Program to reverse an array using temporary array
using System;
class GfG {
// function to reverse an array
static void reverseArray(int[] arr) {
int n = arr.Length;
// Temporary array to store elements in reversed order
int[] temp = new int[n];
// Copy elements from original array to temp in reverse order
for (int i = 0; i < n; i++)
temp[i] = arr[n - i - 1];
// Copy elements back to original array
for (int i = 0; i < n; i++)
arr[i] = temp[i];
}
static void Main() {
int[] arr = { 1, 4, 3, 2, 6, 5 };
reverseArray(arr);
for (int i = 0; i < arr.Length; i++)
Console.Write(arr[i] + " ");
}
}
// JavaScript Program to reverse an array using temporary array
// function to reverse an array
function reverseArray(arr) {
let n = arr.length;
// Temporary array to store elements in reversed order
let temp = new Array(n);
// Copy elements from original array to temp in reverse order
for (let i = 0; i < n; i++)
temp[i] = arr[n - i - 1];
// Copy elements back to original array
for (let i = 0; i < n; i++)
arr[i] = temp[i];
}
const arr = [1, 4, 3, 2, 6, 5];
reverseArray(arr);
console.log(arr.join(" "));
Output
5 6 2 3 4 1
Time Complexity: O(n), Copying elements to a new array is a linear operation.
Auxiliary Space: O(n), as we are using an extra array to store the reversed array.
[Expected Approach – 1] Using Two Pointers – O(n) Time and O(1) Space
The idea is to maintain two pointers: left and right, such that left points at the beginning of the array and right points to the end of the array.
While left pointer is less than the right pointer, swap the elements at these two positions. After each swap, increment the left pointer and decrement the right pointer to move towards the center of array. This will swap all the elements in the first half with their corresponding element in the second half.
Working:
Below is the implementation of the algorithm:
// C++ Program to reverse an array using Two Pointers
#include <iostream>
#include <vector>
using namespace std;
// function to reverse an array
void reverseArray(vector<int> &arr) {
// Initialize left to the beginning and right to the end
int left = 0, right = arr.size() - 1;
// Iterate till left is less than right
while(left < right) {
// Swap the elements at left and right position
swap(arr[left], arr[right]);
// Increment the left pointer
left++;
// Decrement the right pointer
right--;
}
}
int main() {
vector<int> arr = { 1, 4, 3, 2, 6, 5 };
reverseArray(arr);
for(int i = 0; i < arr.size(); i++)
cout << arr[i] << " ";
return 0;
}
// C Program to reverse an array using Two Pointers
#include <stdio.h>
// Function to swap two numbers
void swap(int *a, int *b) {
int temp = *a;
*a = *b;
*b = temp;
}
// function to reverse an array
void reverseArray(int arr[], int n) {
// Initialize left to the beginning and right to the end
int left = 0, right = n - 1;
// Iterate till left is less than right
while (left < right) {
// Swap the elements at left and right position
swap(&arr[left], &arr[right]);
// Increment the left pointer
left++;
// Decrement the right pointer
right--;
}
}
int main() {
int arr[] = { 1, 4, 3, 2, 6, 5 };
int n = sizeof(arr) / sizeof(arr[0]);
reverseArray(arr, n);
for (int i = 0; i < n; i++)
printf("%d ", arr[i]);
return 0;
}
// Java Program to reverse an array using Two Pointers
import java.util.Arrays;
class GfG {
// function to reverse an array
static void reverseArray(int[] arr) {
// Initialize left to the beginning and right to the end
int left = 0, right = arr.length - 1;
// Iterate till left is less than right
while (left < right) {
// Swap the elements at left and right position
int temp = arr[left];
arr[left] = arr[right];
arr[right] = temp;
// Increment the left pointer
left++;
// Decrement the right pointer
right--;
}
}
public static void main(String[] args) {
int[] arr = { 1, 4, 3, 2, 6, 5 };
reverseArray(arr);
for (int i = 0; i < arr.length; i++)
System.out.print(arr[i] + " ");
}
}
# Python Program to reverse an array using Two Pointers
# function to reverse an array
def reverseArray(arr):
# Initialize left to the beginning and right to the end
left = 0
right = len(arr) - 1
# Iterate till left is less than right
while left < right:
# Swap the elements at left and right position
arr[left], arr[right] = arr[right], arr[left]
# Increment the left pointer
left += 1
# Decrement the right pointer
right -= 1
if __name__ == "__main__":
arr = [1, 4, 3, 2, 6, 5]
reverseArray(arr)
for i in range(len(arr)):
print(arr[i], end=" ")
// C# Program to reverse an array using Two Pointers
using System;
class GfG {
// function to reverse an array
static void reverseArray(int[] arr) {
// Initialize left to the beginning and right to the end
int left = 0, right = arr.Length - 1;
// Iterate till left is less than right
while (left < right) {
// Swap the elements at left and right position
int temp = arr[left];
arr[left] = arr[right];
arr[right] = temp;
// Increment the left pointer
left++;
// Decrement the right pointer
right--;
}
}
static void Main() {
int[] arr = { 1, 4, 3, 2, 6, 5 };
reverseArray(arr);
for (int i = 0; i < arr.Length; i++)
Console.Write(arr[i] + " ");
}
}
// JavaScript Program to reverse an array using Two Pointers
// function to reverse an array
function reverseArray(arr) {
// Initialize left to the beginning and right to the end
let left = 0, right = arr.length - 1;
// Iterate till left is less than right
while (left < right) {
// Swap the elements at left and right position
[arr[left], arr[right]] = [arr[right], arr[left]];
// Increment the left pointer
left++;
// Decrement the right pointer
right--;
}
}
const arr = [1, 4, 3, 2, 6, 5];
reverseArray(arr);
console.log(arr.join(" "));
Output
5 6 2 3 4 1
Time Complexity: O(n), as we are visiting each element exactly once.
Auxiliary Space: O(1)
[Expected Approach – 2] By Swapping Elements – O(n) Time and O(1) Space
The idea is to iterate over the first half of the array and swap each element with its corresponding element from the end. So, while iterating over the first half, any element at index i is swapped with the element at index (n – i – 1).
Working:
Below is the implementation of the algorithm:
// C++ Program to reverse an array by swapping elements
#include <iostream>
#include <vector>
using namespace std;
// function to reverse an array
void reverseArray(vector<int> &arr) {
int n = arr.size();
// Iterate over the first half and for every index i,
// swap arr[i] with arr[n - i - 1]
for(int i = 0; i < n/2; i++) {
swap(arr[i], arr[n - i - 1]);
}
}
int main() {
vector<int> arr = { 1, 4, 3, 2, 6, 5 };
reverseArray(arr);
for(int i = 0; i < arr.size(); i++)
cout << arr[i] << " ";
return 0;
}
// C Program to reverse an array by swapping elements
#include <stdio.h>
// function to reverse an array
void reverseArray(int arr[], int n) {
// Iterate over the first half and for every index i,
// swap arr[i] with arr[n - i - 1]
for (int i = 0; i < n / 2; i++) {
int temp = arr[i];
arr[i] = arr[n - i - 1];
arr[n - i - 1] = temp;
}
}
int main() {
int arr[] = { 1, 4, 3, 2, 6, 5 };
int n = sizeof(arr) / sizeof(arr[0]);
reverseArray(arr, n);
for (int i = 0; i < n; i++)
printf("%d ", arr[i]);
return 0;
}
// Java Program to reverse an array by swapping elements
import java.util.Arrays;
class GfG {
// function to reverse an array
static void reverseArray(int[] arr) {
int n = arr.length;
// Iterate over the first half and for every index i,
// swap arr[i] with arr[n - i - 1]
for (int i = 0; i < n / 2; i++) {
int temp = arr[i];
arr[i] = arr[n - i - 1];
arr[n - i - 1] = temp;
}
}
public static void main(String[] args) {
int[] arr = { 1, 4, 3, 2, 6, 5 };
reverseArray(arr);
for (int i = 0; i < arr.length; i++)
System.out.print(arr[i] + " ");
}
}
# Python Program to reverse an array by swapping elements
def reverseArray(arr):
n = len(arr)
# Iterate over the first half and for every index i,
# swap arr[i] with arr[n - i - 1]
for i in range(n // 2):
temp = arr[i]
arr[i] = arr[n - i - 1]
arr[n - i - 1] = temp
if __name__ == "__main__":
arr = [1, 4, 3, 2, 6, 5]
reverseArray(arr)
for i in range(len(arr)):
print(arr[i], end=" ")
// C# Program to reverse an array by swapping elements
using System;
class GfG {
// function to reverse an array
static void reverseArray(int[] arr) {
int n = arr.Length;
// Iterate over the first half and for every index i,
// swap arr[i] with arr[n - i - 1]
for (int i = 0; i < n / 2; i++) {
int temp = arr[i];
arr[i] = arr[n - i - 1];
arr[n - i - 1] = temp;
}
}
static void Main() {
int[] arr = { 1, 4, 3, 2, 6, 5 };
reverseArray(arr);
for (int i = 0; i < arr.Length; i++)
Console.Write(arr[i] + " ");
}
}
// JavaScript Program to reverse an array by swapping elements
// function to reverse an array
function reverseArray(arr) {
let n = arr.length;
// Iterate over the first half and for every index i,
// swap arr[i] with arr[n - i - 1]
for (let i = 0; i < n / 2; i++) {
let temp = arr[i];
arr[i] = arr[n - i - 1];
arr[n - i - 1] = temp;
}
}
const arr = [1, 4, 3, 2, 6, 5];
reverseArray(arr);
console.log(arr.join(" "));
Output
5 6 2 3 4 1
Time Complexity: O(n), the loop runs through half of the array, so it’s linear with respect to the array size.
Auxiliary Space: O(1), no extra space is required, therefore we are reversing the array in-place.
[Alternate Approach] Using Recursion – O(n) Time and O(n) Space
The idea is to use recursion and define a recursive function that takes a range of array elements as input and reverses it. Inside the recursive function,
- Swap the first and last element.
- Recursively call the function with the remaining subarray.
// C++ Program to reverse an array using Recursion
#include <iostream>
#include <vector>
using namespace std;
// recursive function to reverse an array from l to r
void reverseArrayRec(vector<int> &arr, int l, int r) {
if(l >= r)
return;
// Swap the elements at the ends
swap(arr[l], arr[r]);
// Recur for the remaining array
reverseArrayRec(arr, l + 1, r - 1);
}
// function to reverse an array
void reverseArray(vector<int> &arr) {
int n = arr.size();
reverseArrayRec(arr, 0, n - 1);
}
int main() {
vector<int> arr = { 1, 4, 3, 2, 6, 5 };
reverseArray(arr);
for(int i = 0; i < arr.size(); i++)
cout << arr[i] << " ";
return 0;
}
// C Program to reverse an array using Recursion
#include <stdio.h>
// recursive function to reverse an array from l to r
void reverseArrayRec(int arr[], int l, int r) {
if(l >= r)
return;
// Swap the elements at the ends
int temp = arr[l];
arr[l] = arr[r];
arr[r] = temp;
// Recur for the remaining array
reverseArrayRec(arr, l + 1, r - 1);
}
// function to reverse an array
void reverseArray(int arr[], int n) {
reverseArrayRec(arr, 0, n - 1);
}
int main() {
int arr[] = { 1, 4, 3, 2, 6, 5 };
int n = sizeof(arr) / sizeof(arr[0]);
reverseArray(arr, n);
for(int i = 0; i < n; i++)
printf("%d ", arr[i]);
return 0;
}
// Java Program to reverse an array using Recursion
import java.util.Arrays;
class GfG {
// recursive function to reverse an array from l to r
static void reverseArrayRec(int[] arr, int l, int r) {
if (l >= r)
return;
// Swap the elements at the ends
int temp = arr[l];
arr[l] = arr[r];
arr[r] = temp;
// Recur for the remaining array
reverseArrayRec(arr, l + 1, r - 1);
}
// function to reverse an array
static void reverseArray(int[] arr) {
int n = arr.length;
reverseArrayRec(arr, 0, n - 1);
}
public static void main(String[] args) {
int[] arr = { 1, 4, 3, 2, 6, 5 };
reverseArray(arr);
for (int i = 0; i < arr.length; i++)
System.out.print(arr[i] + " ");
}
}
# Python Program to reverse an array using Recursion
# recursive function to reverse an array from l to r
def reverseArrayRec(arr, l, r):
if l >= r:
return
# Swap the elements at the ends
arr[l], arr[r] = arr[r], arr[l]
# Recur for the remaining array
reverseArrayRec(arr, l + 1, r - 1)
# function to reverse an array
def reverseArray(arr):
n = len(arr)
reverseArrayRec(arr, 0, n - 1)
if __name__ == "__main__":
arr = [1, 4, 3, 2, 6, 5]
reverseArray(arr)
for i in range(len(arr)):
print(arr[i], end=" ")
// C# Program to reverse an array using Recursion
using System;
class GfG {
// recursive function to reverse an array from l to r
static void reverseArrayRec(int[] arr, int l, int r) {
if (l >= r)
return;
// Swap the elements at the ends
int temp = arr[l];
arr[l] = arr[r];
arr[r] = temp;
// Recur for the remaining array
reverseArrayRec(arr, l + 1, r - 1);
}
// function to reverse an array
static void reverseArray(int[] arr) {
int n = arr.Length;
reverseArrayRec(arr, 0, n - 1);
}
static void Main(string[] args) {
int[] arr = { 1, 4, 3, 2, 6, 5 };
reverseArray(arr);
for (int i = 0; i < arr.Length; i++)
Console.Write(arr[i] + " ");
}
}
// JavaScript Program to reverse an array using Recursion
// recursive function to reverse an array from l to r
function reverseArrayRec(arr, l, r) {
if (l >= r)
return;
// Swap the elements at the ends
[arr[l], arr[r]] = [arr[r], arr[l]];
// Recur for the remaining array
reverseArrayRec(arr, l + 1, r - 1);
}
// function to reverse an array
function reverseArray(arr) {
let n = arr.length;
reverseArrayRec(arr, 0, n - 1);
}
let arr = [1, 4, 3, 2, 6, 5];
reverseArray(arr);
console.log(arr.join(" "));
Output
5 6 2 3 4 1
Time Complexity: O(n), the recurrence relation will be T(n) = T(n – 2) + O(1), which can be simplified to O(n).
Auxiliary Space: O(n), as we are using recursion stack.
Using Inbuilt Methods – O(n) Time and O(1) Space
The idea is to use inbuilt reverse methods available across different languages.
// C++ Program to reverse an array using inbuilt methods
#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
// function to reverse an array
void reverseArray(vector<int> &arr) {
reverse(arr.begin(), arr.end());
}
int main() {
vector<int> arr = { 1, 4, 3, 2, 6, 5 };
reverseArray(arr);
for(int i = 0; i < arr.size(); i++)
cout << arr[i] << " ";
return 0;
}
// Java Program to reverse an array using inbuilt methods
import java.util.*;
class GfG {
// function to reverse an array
static void reverseArray(List<Integer> arr) {
Collections.reverse(arr);
}
public static void main(String[] args) {
List<Integer> arr =
new ArrayList<>(Arrays.asList(1, 4, 3, 2, 6, 5));
reverseArray(arr);
for (int i = 0; i < arr.size(); i++)
System.out.print(arr.get(i) + " ");
}
}
# Python Program to reverse an array using inbuilt methods
# function to reverse an array
def reverse_array(arr):
arr.reverse()
if __name__ == "__main__":
arr = [1, 4, 3, 2, 6, 5]
reverse_array(arr)
print(" ".join(map(str, arr)))
// C# Program to reverse an array using inbuilt methods
using System;
class GfG {
// function to reverse an array
static void reverseArray(int[] arr) {
Array.Reverse(arr);
}
static void Main() {
int[] arr = { 1, 4, 3, 2, 6, 5 };
reverseArray(arr);
for (int i = 0; i < arr.Length; i++)
Console.Write(arr[i] + " ");
}
}
// JavaScript Program to reverse an array using inbuilt methods
// function to reverse an array
function reverseArray(arr) {
arr.reverse();
}
const arr = [1, 4, 3, 2, 6, 5];
reverseArray(arr);
console.log(arr.join(" "));
Output
5 6 2 3 4 1
Time Complexity: O(n), the reverse method has linear time complexity.
Auxiliary Space: O(1) Additional space is not used to store the reversed array, as the in-built array method swaps the values in-place.
