Swap two numbers without temp variables

Algorithm to swap two numbers without using any extra temp variable.

Everything will be written in ES6.

Example

Input:
a = 1;
b = 2;

Output:
a = 2;
b = 1;

There are many ways we can solve this problem.

• Using arithmetic operations.
• Using logical operations.
• With Array Destructuring.

Using arithmetic operations

Implementation

• We are going to subtract a from b and store it in b, b = b – a
• Then we are going to add a and b and store it in a, a = a + b
• And in the end we are going to subtract b from a and store it in b, b = a – b

//function to swap to numbers without any temp variable
 function swapNumbers(a, b){
   console.log('Before swapping a = '+a+' and b = '+b);
   b = b - a;
   a = a + b;
   b = a - b;
   console.log('After swapping a = '+a+' and b = '+b);
 }

Input:
swapNumbers(10, 15);

Output:
//How this works
/*Step 1*/ b = b - a = 15 - 10 = 5. /*So b = 5*/ 
/*Step 2*/ a = a + b = 10 + 5 = 15. /*So a = 15*/ 
/*Step 3*/ b = a - b = 15 - 5 = 10. /*So b = 10*/ 

Before swapping a = 10 and b = 15
After swapping a = 15 and b = 10

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

Time and Space complexity

• We are solving this with only arithmetic operations, Time Complexity is O(1).
• We are using only constant space, Space Complexity is O(1).

Using logical operations

Implementation

• We are going to solve this problem using bitwise XOR, XOR returns 1 if two bits are different i.e 1 ^ 0 will return 1, same bits will return 0.
• We are going to perform logical XOR on a and b and store it in a, a = a ^ b
• Then we are going to perform XOR on a and b and store it in b, b = a ^ b
• And in the end we are going to perform XOR on a and b and store it in a, a = a ^ b

//function to swap to numbers without any temp variable
 function swapNumbers(a, b){
   console.log('Before swapping a = '+a+' and b = '+b);
   a = a ^ b;
   b = a ^ b;
   a = a ^ b;
   console.log('After swapping a = '+a+' and b = '+b);
 }

Input:
swapNumbers(10, 15);

Output:
//How this works
/*Step 1*/ a = a ^ b = 00001111 ^ 00001010 = 00000101 = 5. /*So a = 5*/ 
/*Step 2*/ b = a ^ b = 00000101 ^ 00001010 = 00001111 = 15. /*So b = 15*/ 
/*Step 3*/ a = a ^ b = 00000101 ^ 00001111 = 00001010 = 10. /*So a = 10*/ 

Before swapping a = 10 and b = 15
After swapping a = 15 and b = 10

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

Time and Space complexity

• We are solving this with only XOR, Time Complexity is O(1).
• We are using only constant space, Space Complexity is O(1).

With Array Destructuring

We will use Destructuring to swap two numbers with using any temp variables.

//function to swap to numbers without any temp variable
 function swapNumbers(a, b){
   console.log('Before swapping a = '+a+' and b = '+b);
   [a, b] = [b, a];
   console.log('After swapping a = '+a+' and b = '+b);
 }

Input:
swapNumbers(10, 15);

Output:
Before swapping a = 10 and b = 15
After swapping a = 15 and b = 10

Time complexity: O(1).
Space complexity: O(1).

Time and Space complexity

• We are using array Destructuring to swap numbers, so Time complexity is O(1).
• We are using constant space, so Space complexity is O(1).