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.
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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