Swap every pair of characters in string

Question

I'd like to get all the permutations of swapped characters pairs of a string. For example:

Base string: abcd Combinations:

1. bacd
2. acbd
3. abdc

etc.

What's the best way to do this?

Answer 1

Edit: Markdown hates me today...

$input = "abcd";
$len = strlen($input);
$output = array();

for ($i = 0; $i < $len - 1; ++$i) {
    $output[] = substr($input, 0, $i)
              . substr($input, $i + 1, 1)
              . substr($input, $i, 1)
              . substr($input, $i + 2);
}
print_r($output);

Answer 2

Related concept: Damerau–Levenshtein distance.

Answer 3

nickf made beautiful solution thank you , i came up with less beautiful:

  $arr=array(0=>'a',1=>'b',2=>'c',3=>'d');
  for($i=0;$i<count($arr)-1;$i++){
  $swapped="";
  //Make normal before swapped
  for($z=0;$z<$i;$z++){
   $swapped.=$arr[$z];
  }
  //Create swapped
  $i1=$i+1;
  $swapped.=$arr[$i1].$arr[$i];

  //Make normal after swapped.     
  for($y=$z+2;$y<count($arr);$y++){
  $swapped.=$arr[$y];

  }
$arrayswapped[$i]=$swapped;
}
var_dump($arrayswapped);

Answer 4

A fast search in google gave me that:

http://cogo.wordpress.com/2008/01/08/string-permutation-in-php/

Answer 5

How about just using the following:

function swap($s, $i)
{
  $t = $s[$i];
  $s[$i] = $s[$i+1];
  $s[$i+1] = $t;

  return $s;
}

$s = "abcd";
$l = strlen($s);
for ($i=0; $i<$l-1; ++$i)
{
  print swap($s,$i)."\n";
}

Answer 6

Here is a slightly faster solution as its not overusing substr().

function swapcharpairs($input = "abcd") {
  $pre = "";
  $a="";
  $b = $input[0];
  $post = substr($input, 1);
  while($post!='') {
    $pre.=$a;
    $a=$b;
    $b=$post[0];
    $post=substr($post,1);
    $swaps[] = $pre.$b.$a.$post;
  };
  return $swaps;
}

print_R(swapcharpairs());