Swap Two Numbers Without Using Third Variable

Try it on GfG Practice

Given two variables a and y, swap two variables without using a third variable. 

Examples:

Input: a = 2, b = 3
Output: a = 3, b = 2

Input: a = 20, b = 0
Output: a = 0, b = 20

Input: a = 10, b = 10
Output: a = 10, b = 10

Using Arithmetic Operators

• Store the sum of a and b in a (a = a + b).
• Get the original value of a, that is (sum - original value of b)and store it in b (b = a - b).
• Get the original value of b, that is (sum - original value of a)and store it in a (a = a - b).

// C++ Code to swap two numbers using arithmetic operators

#include <iostream>
using namespace std;

int main() {
    int a = 2, b = 3;
    cout << "a = " << a << " b = " << b << endl;   
  
    a = a + b;
    b = a - b;
    a = a - b;
  
    cout << "a = " << a << " b = " << b << endl;
    return 0;
}

// C Code to swap two numbers using arithmetic operators

#include <stdio.h>
int main() {
    int a = 2, b = 3;
    printf("a = %d b = %d\n", a, b);   
  
    a = a + b;
    b = a - b;
    a = a - b;
  
    printf("a = %d b = %d\n", a, b);
    return 0;
}

// Java Code to swap two numbers using arithmetic operators

class GfG {
    public static void main(String[] args) {
        int a = 2, b = 3;
        System.out.println("a = " + a + " b = " + b);   
      
        a = a + b;
        b = a - b;
        a = a - b;
      
        System.out.println("a = " + a + " b = " + b);
    }
}

# Python Code to swap two numbers using arithmetic operators

if __name__ == "__main__":
	a = 2
	b = 3
	print("a =", a, " b =", b)
    
	a = a + b
	b = a - b
	a = a - b
    
	print("a =", a, " b =", b)

// C# Code to swap two numbers using arithmetic operators

using System;

class GfG {
    static void Main() {
        int a = 2, b = 3;
        Console.WriteLine("a = " + a + " b = " + b);   
      
        // Swap a and b using arithmetic operators
        a = a + b;
        b = a - b;
        a = a - b;
      
        Console.WriteLine("a = " + a + " b = " + b);
    }
}

// JavaScript Code to swap two numbers using arithmetic operators

let a = 2, b = 3;
console.log("a = " + a + " b = " + b);   

a = a + b;
b = a - b;
a = a - b;

console.log("a = " + a + " b = " + b);

a = 2 b = 3
a = 3 b = 2

Time Complexity: O(1)
Auxiliary Space: O(1)

Using Bitwise XOR

The idea is to use the properties of XOR to swap the two variables.

• a = a ^ b: Store the Bitwise XOR of a and b in a. Now, a holds the result of (a ^ b).
• b = a ^ b: Bitwise XOR the new value of a with b to get the original value of a. This gives us, b = (a ^ b) ^ b = a.
• a = a ^ b: Bitwise XOR the new value of a with the new value of b (which is the original a) to get the original value of b. This gives us, a = (a ^ b) ^ a = b.

Finally, a and b hold the swapped values.

// C++ Code to swap two numbers using bitwise XOR

#include <iostream>
using namespace std;

int main() {
    int a = 2, b = 3;
    cout << "a = " << a << " b = " << b << endl;   
  
    a = a ^ b;
    b = a ^ b;
    a = a ^ b;
  
    cout << "a = " << a << " b = " << b << endl;
    return 0;
}

// C Code to swap two numbers using bitwise XOR

#include <stdio.h>
int main() {
    int a = 2, b = 3;
    printf("a = %d b = %d\n", a, b);   
  
    a = a ^ b;
    b = a ^ b;
    a = a ^ b;
  
    printf("a = %d b = %d\n", a, b);
    return 0;
}

// Java Code to swap two numbers using bitwise XOR

class GfG {
    public static void main(String[] args) {
        int a = 2, b = 3;
        System.out.println("a = " + a + " b = " + b);   
      
        a = a ^ b;
        b = a ^ b;
        a = a ^ b;
      
        System.out.println("a = " + a + " b = " + b);
    }
}

# Python Code to swap two numbers using bitwise XOR

if __name__ == "__main__":
	a = 2
	b = 3
	print("a =", a, " b =", b)
    
	a = a ^ b
	b = a ^ b
	a = a ^ b
    
	print("a =", a, " b =", b)

// C# Code to swap two numbers using bitwise XOR

using System;

class GfG {
    static void Main() {
        int a = 2, b = 3;
        Console.WriteLine("a = " + a + " b = " + b);   
      
        // Swap a and b using arithmetic operators
        a = a ^ b;
        b = a ^ b;
        a = a ^ b;
      
        Console.WriteLine("a = " + a + " b = " + b);
    }
}

// JavaScript Code to swap two numbers using bitwise XOR

let a = 2, b = 3;
console.log("a = " + a + " b = " + b);   

a = a ^ b;
b = a ^ b;
a = a ^ b;

console.log("a = " + a + " b = " + b);

a = 2 b = 3
a = 3 b = 2

Time Complexity: O(1)
Auxiliary Space: O(1)

Built-in Swap

We can also swap using built-in functionalities like swap method in C++, tuple unpacking in Python, destructuring assignment in JavaScript. To know more about the implementation, please refer Swap Two Numbers.