# 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 note use ‘-‘ operator.

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

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 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++ 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;
}

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++ 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)
{
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
// 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;
}

Output:

6 1 2 7 3 5

### Asked in: Infosys, Moonfrog Labs

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