Reverse an array without using subtract sign ‘-‘ anywhere in the code

Given an array, the task is to reverse the array without using subtract sign ‘-‘ anywhere in your code. It is not tough to reverse an array but the main thing is to not use ‘-‘ operator.

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

Asked in: Moonfrog Interview

Below are different approaches:

Method 1:
1- Store array elements into a vector in C++.
2- Then reverse the vector using predefined functions.
3- Then store reversed elements into the array back.

Method 2:
1- Store array elements into a stack.
2- As the stack follows Last In First Out, so we can store elements from
top of the stack into the array which will be itself in a reverse manner.

Method 3:
1- In this method, the idea is to use a negative sign but by storing it into a variable.
2- By using this statement x = (INT_MIN/INT_MAX), we get -1 in a variable x.
3- As INT_MIN and INT_MAX have same values just of opposite signs, so on dividing them it will give -1.
4- Then ‘x’ can be used in decrementing the index from last.

C++

// C++ program to reverse an array without 
// using "-" sign 
#include <bits/stdc++.h> 
using namespace std; 
  
// Function to reverse array 
void reverseArray(int arr[], int n) 
{ 
    // Trick to assign -1 to a variable 
    int x = (INT_MIN / INT_MAX); 
  
    // Reverse array in simple manner 
    for (int i = 0; i < n / 2; i++) 
  
        // Swap ith index value with (n-i-1)th 
        // index value 
        swap(arr[i], arr[n + (x * i) + x]); 
} 
  
// Drivers code 
int main() 
{ 
    int arr[] = { 5, 3, 7, 2, 1, 6 }; 
    int n = sizeof(arr) / sizeof(arr[0]); 
  
    reverseArray(arr, n); 
  
    // print the reversed array 
    for (int i = 0; i < n; i++) 
        cout << arr[i] << " "; 
  
    return 0; 
} 

Java

// Java program to reverse an array without 
// using "-" sign 
class GFG { 
  
    // Function to reverse array 
    static void reverseArray(int arr[], int n) 
    { 
        // Trick to assign -1 to a variable 
        int x = (Integer.MIN_VALUE / Integer.MAX_VALUE); 
  
        // Reverse array in simple manner 
        for (int i = 0; i < n / 2; i++) 
  
            // Swap ith index value with (n-i-1)th 
            // index value 
            swap(arr, i, n + (x * i) + x); 
    } 
    static int[] swap(int[] arr, int i, int j) 
    { 
        int temp = arr[i]; 
        arr[i] = arr[j]; 
        arr[j] = temp; 
        return arr; 
    } 
  
    // Drivers code 
    public static void main(String[] args) 
    { 
        int arr[] = { 5, 3, 7, 2, 1, 6 }; 
        int n = arr.length; 
  
        reverseArray(arr, n); 
  
        // print the reversed array 
        for (int i = 0; i < n; i++) 
            System.out.print(arr[i] + " "); 
    } 
} 
  
// This code has been contributed by 29AjayKumar 

Python3

# Python program to reverse an array without 
# using "-" sign 
  
# Function to reverse array 
def reverseArray(arr, n): 
  
    import sys 
  
    # Trick to assign - 1 to a variable 
    x = -sys.maxsize // sys.maxsize 
  
    # Reverse array in simple manner 
    for i in range(n//2): 
  
        # Swap ith index value with (n-i-1)th 
        # index value 
        arr[i], arr[n + (x*i) + x] = arr[n + (x*i) + x], arr[i] 
  
  
# Driver code 
if __name__ == "__main__": 
    arr = [5, 3, 7, 2, 1, 6] 
    n = len(arr) 
  
    reverseArray(arr, n) 
  
    # print the reversed array 
    for i in range(n): 
        print(arr[i], end=" ") 
  
# This code is contributed by 
# sanjeev2552 

C#

// C# program to reverse an array without 
// using "-" sign 
using System; 
  
class GFG { 
  
    // Function to reverse array 
    static void reverseArray(int[] arr, int n) 
    { 
        // Trick to assign -1 to a variable 
        int x = (int.MinValue / int.MaxValue); 
  
        // Reverse array in simple manner 
        for (int i = 0; i < n / 2; i++) 
  
            // Swap ith index value with (n-i-1)th 
            // index value 
            swap(arr, i, n + (x * i) + x); 
    } 
  
    static int[] swap(int[] arr, int i, int j) 
    { 
        int temp = arr[i]; 
        arr[i] = arr[j]; 
        arr[j] = temp; 
        return arr; 
    } 
  
    // Drivers code 
    public static void Main() 
    { 
        int[] arr = { 5, 3, 7, 2, 1, 6 }; 
        int n = arr.Length; 
  
        reverseArray(arr, n); 
  
        // print the reversed array 
        for (int i = 0; i < n; i++) 
            Console.Write(arr[i] + " "); 
    } 
} 
  
/* This code contributed by PrinciRaj1992 */

PHP

<?PHP 
// PHP program to reverse an array without 
// using "-" sign 
  
// Function to reverse array 
function reverseArray(&$arr, $n) 
{ 
    // Trick to assign -1 to a variable 
    $x = (PHP_INT_MIN / PHP_INT_MAX); 
  
    // Reverse array in simple manner 
    for ($i = 0; $i < $n / 2; $i++) 
  
        // Swap ith index value with (n-i-1)th 
        // index value 
        swap($arr, $i, $n + ($x * $i) + $x); 
} 
  
function swap(&$arr, $i, $j) 
{ 
    $temp = $arr[$i]; 
    $arr[$i] = $arr[$j]; 
    $arr[$j] = $temp; 
    return $arr; 
} 
  
// Drivers code 
$arr = array( 5, 3, 7, 2, 1, 6 ); 
$n = sizeof($arr); 
  
reverseArray($arr, $n); 
  
// print the reversed array 
for ($i = 0; $i < $n; $i++) 
    echo($arr[$i] . " "); 
  
// This code is contributed by Code_Mech 

Output:

6 1 2 7 3 5

Method 4:
In this method 4, the idea is to use bitwise operator to implement subtraction i.e.
A – B = A + ~B + 1
so, i– can be written as i = i +~1 +1

C++

// C++ program to reverse an array without 
// using "-" sign 
#include <bits/stdc++.h> 
using namespace std; 
  
// Function to reverse array 
void reverseArray(int arr[], int n) 
{ 
  
    // Reverse array in simple manner 
    for (int i = 0; i < n / 2; i++) 
  
        // Swap ith index value with (n-i-1)th 
        // index value 
        // Note : A - B = A + ~B + 1 
        // So n - i = n + ~i + 1 then 
        // n - i - 1 = (n + ~i + 1) + ~1 + 1 
        swap(arr[i], arr[(n + ~i + 1) + ~1 + 1]); 
} 
  
// Driver code 
int main() 
{ 
    int arr[] = { 5, 3, 7, 2, 1, 6 }; 
    int n = sizeof(arr) / sizeof(arr[0]); 
  
    reverseArray(arr, n); 
  
    // print the reversed array 
    for (int i = 0; i < n; i++) 
        cout << arr[i] << " "; 
  
    return 0; 
} 

Java

// Java program to reverse an array without 
// using "-" sign 
import java.util.Arrays; 
  
class GFG { 
  
    // Function to reverse array 
    static void reverseArray(int arr[], int n) 
    { 
     
        // Reverse array in simple manner 
        for (int i = 0; i < n / 2; i++) 
  
        // Swap ith index value with (n-i-1)th 
        // index value 
        // Note : A - B = A + ~B + 1 
        // So n - i = n + ~i + 1 then 
        // n - i - 1 = (n + ~i + 1) + ~1 + 1 
        { 
            swap(arr, i, (n + ~i + 1) + ~1 + 1); 
        } 
    } 
  
    static int[] swap(int[] arr, int i, int j) 
    { 
        int temp = arr[i]; 
        arr[i] = arr[j]; 
        arr[j] = temp; 
        return arr; 
    } 
  
    // Driver code 
    public static void main(String args[]) 
    { 
        int arr[] = { 5, 3, 7, 2, 1, 6 }; 
        int n = arr.length; 
  
        reverseArray(arr, n); 
  
        // print the reversed array 
        for (int i = 0; i < n; i++) { 
            System.out.print(arr[i] + " "); 
        } 
    } 
} 
  
// This code contributed by Rajput-Ji 

Python3

# Python program to reverse an array without  
# using "-" sign  
  
# Function to reverse array  
def reverseArray(arr, n): 
  
    # Reverse array in simple manner  
    for i in range(n//2):  
  
        # Swap ith index value with (n-i-1)th  
        # index value  
        # Note : A - B = A + ~B + 1  
        # So n - i = n + ~i + 1 then  
        # n - i - 1 = (n + ~i + 1) + ~1 + 1  
        arr[i], arr[(n + ~i + 1) + ~1 + 1] = arr[(n + ~i + 1) + ~1 + 1],arr[i] 
  
# Driver code  
  
arr = [ 5, 3, 7, 2, 1, 6 ]  
n = len(arr) 
  
reverseArray(arr, n) 
  
# print the reversed array  
for i in range(n): 
    print(arr[i],end=" ") 
  
# This code is contributed by ankush_953 

C#

// C# program to reverse an array without 
// using "-" sign 
using System; 
  
class GFG { 
  
    // Function to reverse array 
    static void reverseArray(int[] arr, int n) 
    { 
  
        // Reverse array in simple manner 
        for (int i = 0; i < n / 2; i++) 
  
        // Swap ith index value with (n-i-1)th 
        // index value 
        // Note : A - B = A + ~B + 1 
        // So n - i = n + ~i + 1 then 
        // n - i - 1 = (n + ~i + 1) + ~1 + 1 
        { 
            swap(arr, i, (n + ~i + 1) + ~1 + 1); 
        } 
    } 
  
    static int[] swap(int[] arr, int i, int j) 
    { 
        int temp = arr[i]; 
        arr[i] = arr[j]; 
        arr[j] = temp; 
        return arr; 
    } 
  
    // Driver code 
    public static void Main(String[] args) 
    { 
        int[] arr = { 5, 3, 7, 2, 1, 6 }; 
        int n = arr.Length; 
  
        reverseArray(arr, n); 
  
        // print the reversed array 
        for (int i = 0; i < n; i++) { 
            Console.Write(arr[i] + " "); 
        } 
    } 
} 
  
// This code has been contributed by 29AjayKumar 

PHP

<?PHP 
    // PHP program to reverse an array without 
    // using "-" sign 
      
    // Function to reverse array 
    function reverseArray(&$arr, $n) 
    { 
  
        // Reverse array in simple manner 
        for ($i = 0; $i < $n / 2; $i++) 
  
        // Swap ith index value with (n-i-1)th 
        // index value 
        // Note : A - B = A + ~B + 1 
        // So n - i = n + ~i + 1 then 
        // n - i - 1 = (n + ~i + 1) + 1 + 1 
        { 
            swap($arr, $i, ($n + ~$i + 1) + ~1 + 1); 
        } 
    } 
  
    function swap(&$arr, $i, $j) 
    { 
        $temp = $arr[$i]; 
        $arr[$i] = $arr[$j]; 
        $arr[$j] = $temp; 
        return $arr; 
    } 
  
    // Driver code 
    { 
        $arr = array( 5, 3, 7, 2, 1, 6 ); 
        $n = sizeof($arr); 
  
        reverseArray($arr, $n); 
  
        // print the reversed array 
        for ($i = 0; $i < $n; $i++) 
        { 
            echo($arr[$i] . " "); 
        } 
    } 
  
// This code contributed by Code_Mech 

Output:

6 1 2 7 3 5

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My Personal Notes

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

C++

Java

Python3

C#

PHP

C++

Java

Python3

C#

PHP

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