Python Program to Swap Two Numbers Without Temp Variable

You can swap two numbers without a temp variable in Python using arithmetic: a = a + b; b = a - b; a = a - b or tuple unpacking: a, b = b, a.

Examples

Inputa=3, b=5

Outputa=5, b=3

Inputa=0, b=0

Outputa=0, b=0

Inputa=-10, b=20

Outputa=20, b=-10

How to Think About It

To swap two numbers without a temporary variable, think about how you can use math operations or Python's ability to assign multiple variables at once. Using addition and subtraction, you combine the values and then separate them again to swap. Alternatively, Python allows swapping directly with tuple unpacking, which is simple and clean.

Algorithm

1

Get the two numbers a and b

2

Add b to a and store in a

3

Subtract new a by b to get original a and assign to b

4

Subtract new a by new b to get original b and assign to a

5

Now a and b are swapped

Code

python

a = 3
b = 5

# Swap without temp variable using arithmetic
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=3, b=5
After swap: a=5, b=3

Dry Run

Let's trace swapping a=3 and b=5 through the arithmetic method

1

Initial values

a=3, b=5

2

Add b to a

a = 3 + 5 = 8

3

Subtract new a by b to get original a

b = 8 - 5 = 3

4

Subtract new a by new b to get original b

a = 8 - 3 = 5

5

Swapped values

a=5, b=3

Step	a	b
Initial	3	5
a = a + b	8	5
b = a - b	8	3
a = a - b	5	3

Why This Works

Step 1: Combine values

Adding a + b stores the total in a, holding both values combined.

Step 2: Extract original a

Subtracting a - b gives the original b value, which we assign to b.

Step 3: Extract original b

Subtracting a - b again gives the original a value, which we assign to a.

Alternative Approaches

Tuple unpacking

python

a = 3
b = 5
print(f'Before swap: a={a}, b={b}')
a, b = b, a
print(f'After swap: a={a}, b={b}')

This is the simplest and most Pythonic way, using Python's multiple assignment feature.

Using XOR bitwise operator

python

a = 3
b = 5
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}')

This method works only with integers and uses bitwise XOR to swap without extra space.

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

Time Complexity

Swapping two numbers involves a fixed number of operations, so it runs in constant time O(1).

Space Complexity

No extra memory is used beyond the variables themselves, so space complexity is O(1).

Which Approach is Fastest?

Tuple unpacking is fastest and most readable in Python, while arithmetic and XOR methods are alternatives but less clear.

Approach	Time	Space	Best For
Arithmetic	O(1)	O(1)	Numeric types, no extra variable
Tuple unpacking	O(1)	O(1)	All types, most readable
XOR bitwise	O(1)	O(1)	Integers only, low-level operations