Ninedays Blog

When talking to a friend of mine, Tim, one day he was challenging my programmer knowledge. He of course pulled out the all time "Swap 2 variables in 1 line without using a temporary variable."

Of course I didn't know the answer. There's rarely a need for this application with what I do, for me it appears to be more of a trivia item or an interview question.

Either way I was sitting here watching trashy VH1 reality TV shows and surfing MySpace when I realized I had not learned anything today.

So I Googled and learned about PHP: bitwise operators and that this one line would swap two variables without a temporary variable.

The One Line Swap

PHP

$x ^= $y ^= $x ^= $y;

I wrote a quick function for something like this too!

PHP

function swap($x, $y) {
    $x ^= $y ^= $x ^= $y;
    return array($x,$y);
}

Once you get to the function you are using more than one line and possibly taking more processing power but it's a good library piece.

My Test Script

The whole script I was testing and playing with looked like this:

PHP

<?php
    function swap($x, $y) {
        $x ^= $y ^= $x ^= $y;
        return array($x,$y);
    }

    $x = 6;
    $y = 2;

    echo 'y: ' . $y . ' x: ' . $x;
    // Prints 'y: 2 x: 6

    // Using a function
    list($x, $y) = swap($x, $y);

    echo 'y: ' . $y . ' x: ' . $x;
    // Prints 'y: 6 x: 2

    // Using inline operators
    $x ^= $y ^= $x ^= $y;

    echo 'y: ' . $y . ' x: ' . $x;
    // Prints 'y: 2 x: 6

?>

Good stuff huh?

Update 12/27/2007 new

Easier 1 Line 2 var Swap

And then one day while perusing the internet I found an even easier solution on Optimus Pete - PHP Swap Variables One Liner.

PHP

<?php
    list($x,$y) = array($y,$x); 
?>

Way easier than my function, though live and learn. At least now through exploration I know more about PHP's XOR swapping.

Additional Resources

• How to swap two variables, without using third variable
• PHP Assignment Operators
• Using PHP Operators
• PHP Swap Variables One Liner new
• PHP XOR Swap Speed - Benchmark Test new