Python Program to Swap Two Numbers Using XOR

You can swap two numbers a and b in Python using XOR with: a = a ^ b; b = a ^ b; a = a ^ b.

Examples

Inputa=5, b=10

OutputAfter swap: a=10, b=5

Inputa=0, b=0

OutputAfter swap: a=0, b=0

Inputa=123, b=456

OutputAfter swap: a=456, b=123

How to Think About It

To swap two numbers without using a temporary variable, use the XOR operator which flips bits where the bits differ. By applying XOR three times in a specific order, the values get exchanged without extra space.

Algorithm

1

Take two numbers a and b.

2

Set a to a XOR b.

3

Set b to a XOR b (which is original a).

4

Set a to a XOR b (which is original b).

5

Now a and b are swapped.

Code

python

a = 5
b = 10
print(f"Before swap: a={a}, b={b}")
a = a ^ b
b = a ^ b
a = a ^ b
print(f"After swap: a={a}, b={b}")

Output

Before swap: a=5, b=10
After swap: a=10, b=5

Dry Run

Let's trace swapping a=5 and b=10 using XOR.

1

Initial values

a=5 (0101), b=10 (1010)

2

a = a ^ b

a = 0101 ^ 1010 = 1111 (15)

3

b = a ^ b

b = 1111 ^ 1010 = 0101 (5) (original a)

4

a = a ^ b

a = 1111 ^ 0101 = 1010 (10) (original b)

Step	a (binary)	b (binary)	a (decimal)	b (decimal)
Initial	0101	1010	5	10
a = a ^ b	1111	1010	15	10
b = a ^ b	1111	0101	15	5
a = a ^ b	1010	0101	10	5

Why This Works

Step 1: XOR basics

The XOR operator ^ returns 1 only when bits differ, which helps encode differences between numbers.

Step 2: First XOR stores combined info

Setting a = a ^ b stores combined info of both numbers in a.

Step 3: Recover original a in b

Then b = a ^ b uses combined info to get original a value into b.

Step 4: Recover original b in a

Finally, a = a ^ b recovers original b value into a, completing the swap.

Alternative Approaches

Using a temporary variable

python

a = 5
b = 10
temp = a
a = b
b = temp
print(f"After swap: a={a}, b={b}")

Simple and clear but uses extra memory for temp variable.

Using tuple unpacking

python

a = 5
b = 10
a, b = b, a
print(f"After swap: a={a}, b={b}")

Pythonic and concise, no extra variables needed.

Complexity: O(1) time, O(1) space

Time Complexity

Swapping using XOR involves a fixed number of operations, so it runs in constant time.

Space Complexity

No extra memory is used besides the input variables, so space complexity is constant.

Which Approach is Fastest?

All methods run in constant time; tuple unpacking is most readable, XOR uses no extra memory, and temporary variable is simplest to understand.

Approach	Time	Space	Best For
XOR Swap	O(1)	O(1)	Memory-constrained environments
Temporary Variable	O(1)	O(1)	Clarity and simplicity
Tuple Unpacking	O(1)	O(1)	Pythonic and readable code