Variable a=10,b=20, Realize the exchange of two variable values without the help of the third variable .

1、 Arithmetic operations

I saw this problem a long time ago , At that time, I only knew that it was XOR ^ solve , Later, I also saw that someone used addition and subtraction or multiplication and division to solve , This arithmetic operation is easy to understand, and the code is posted below .

Add and subtract to achieve ：

a = 10
b = 20
a = a + b
b = a - b
a = a - b
print(a, b)  # 20 10

Multiplication and division implementation ：

a = 10
b = 20
a = a * b
b = a / b
a = a / b
print(a, b)  # 20.0 10.0  The decimal point is because python The result of middle division is floating point 

2、 Exclusive or (^)

A simple overview of XOR is that the same is false (0), Difference is true (1).

The key point of XOR operation is ： hypothesis a^b=c, be c^b=a,c^a=b, That is to say, a number is exclusive or the same number twice, and the result remains the same .

We all know that the data in the computer is stored in binary form , Now let's assume two variables at random a, b Binary system ,a=101101,b=001010,a^b^b=a^(b^b), And according to the definition of XOR , Any number and its own XOR will be equal to 0, For example, the above b^b=001010^001010=000000. Also according to the definition of XOR , Any number and 0 XOR will be equal to the number itself , It's like a^0=101101^000000=101101.

Figured out the logic of XOR , The code is easy to write

#  XOR implementation 
a = 10
b = 20
a = a ^ b
b = a ^ b
a = a ^ b
print(a, b)  # 20 10

3、python Unpacking in

a = 10
b = 20
a, b = b, a
print(a, b)  # 20 10