CODEWITHSUNDEEP
algorithmxor
user2714358
user2714358

Reputation: 595

swapping three numbers using xor in a single line

I read that three variables a,b, and c can be swapped using the single statement below: c = a ^ b ^ c ^ (a=b) ^ (b=c)

Similarly, two variables a and b can be swapped as: a = a ^ b ^ (b=a)

Can somebody please explain how does this work?

P.S. Here is the link saying so. http://p--np.blogspot.ro/2011/04/reverse-linked-list-using-only-2.html

Upvotes: 3

Views: 431

Answers (1)

amit
amit

Reputation: 178461

You only need to make in the original statement all assignments (except the one you want to change to) are countered:

a = a ^ b ^ c ^ (b=c) ^ (c=a);

You assign c=a, b=c. The return value of those is a and c respectevely, so, you want to "counter" a and c, and you use the fact that a^a == 0 and c^c == 0, and just add a,c at the beginning.
In addition, you add a b, to assign a to the value of b.

Here is a demo on ideone

Note that as discussed in comments, it is language dependent if the above is guaranteed to succeed or not. In Java, for example - it is: The Java programming language guarantees that the operands of operators appear to be evaluated in a specific evaluation order, namely, from left to right., while in others, such as C, it is not.

Upvotes: 1

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