On: Why we don't hire programmers based on puzzles and tricks

[zeteo]

Come to think of it, swapping two variables in place is a horrible question - because you can't really do it! A statement like

a = a + b

requires the (invisible) presence of a register where a + b (or xor or whatever) is placed right before being written back to a. But then you might as well use this register directly for the swap instead of dabbling around with one-to-one functions.

[steveklabnik → zeteo]

Also, it depends on which language you're using...

    $ irb
    irb(main):001:0> a = 1
    => 1
    irb(main):002:0> b = 2
    => 2
    irb(main):003:0> b, a = a, b
    => [1, 2]
    irb(main):004:0> puts "#{a} #{b}"
    2 1
    => nil

(obviously this has the same flaw you mention, the interpreter is doing stuff for you. It follows the letter of the 'no intermediate variables' only.)

[michaelfairley → steveklabnik]

You can also follow the letter in C, Java, etc.:

  a ^= b
  b ^= a
  a ^= b

[jervisfm → michaelfairley]

What does that do?

[steveklabnik → jervisfm]

http://en.wikipedia.org/wiki/XOR_swap_algorithm

[jervisfm → steveklabnik]

Thanks for the pointer.

[simcop2387 → zeteo]

Just to add a perl version for the ruby and python ones.

($a, $b) = ($b, $a)

[chris_mahan → zeteo]

python: a, b = b, a