Python - Swap two numbers without using Temporary Variable


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The value of two variables can be swapped without using any temporary variables. The method involves using operators like +, *, / and bitwise.

Example: Using + operator

In the below example, the + operator is used to swap the value of two variables x and y.

def swap(x, y):
  print("Before Swap.")
  print("x =",x)
  print("y =",y)

  #Swap technique
  x = x + y
  y = x - y
  x = x - y

  print("After Swap.")
  print("x =",x)
  print("y =",y)

swap(10, 25)

Output

Before Swap.
x = 10
y = 25
After Swap.
x = 25
y = 10

Example: Using * operator

Like + operator, the * operator can also be used to swap the value of two variables x and y.

def swap(x, y):
  print("Before Swap.")
  print("x =",x)
  print("y =",y)

  #Swap technique
  x = x * y
  y = x / y
  x = x / y

  print("After Swap.")
  print("x =",x)
  print("y =",y)

swap(10, 25)

Output

Before Swap.
x = 10
y = 25
After Swap.
x = 25
y = 10

Example: Using / operator

Smilarly / operator can also be used to swap the value of two variables x and y.

def swap(x, y):
  print("Before Swap.")
  print("x =",x)
  print("y =",y)

  #Swap technique
  x = x / y
  y = x * y
  x = y / x

  print("After Swap.")
  print("x =",x)
  print("y =",y)

swap(10, 25)

Output

Before Swap.
x = 10
y = 25
After Swap.
x = 25
y = 10

Example: Using bitwise operator

The bitwise XOR (^) operator can also be used to swap the value of two variables x and y. It returns 1 when one of two bits at same position in both operands is 1, otherwise returns 0.

def swap(x, y):
  print("Before Swap.")
  print("x =",x)
  print("y =",y)

  #Swap technique
  x = x ^ y
  y = x ^ y
  x = y ^ x

  print("After Swap.")
  print("x =",x)
  print("y =",y)

swap(10, 25)

Output

Before Swap.
x = 10
y = 25
After Swap.
x = 25
y = 10

Disadvantages of using above methods

  • The multiplication and division based approaches fail if the value of one of the variable is 0.
  • The addition based approach may fail due to arithmetic overflow. If x and y are too large, operation performed on operands may result into out of range integer.



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