A hard problem

[Anon]

I have an amount of character pairs (ex. Rr,Ss,Tt). It doesn't matter what they exactly are, each could be in a array ($char[1][1]="R";$char[1][2]="r"...)
What I want to get is all different combinations of one letter in each pair with each character from the other pairs.

Example:
1) Rr,SS would return RS, RS, rS, rS

2) Rr,Ss,TT would return
RST
RSt
Rst
Rst
rST
rSt
rst
rst

Remember there could be any amount of pairs.

Thanks a lot.

[Anon]

Hi,

A solution could be this one:

<?php

function rest ($arr) {
if (sizeof($arr) == 0)
return FALSE;

if (sizeof($arr) == 1) {
$fin[] = $arr[0][0];
$fin[] = $arr[0][1];
}
else {
// create an auxiliary array with the elements arr[1..n][]
for ($i = 1; $i < sizeof($arr); ++$i)
$arr_aux[$i-1] = $arr[$i];

// obtain the combinations of the rest of the array
$rest_aux = rest ($arr_aux);

// make the combination with the first elements
for ($i = 0; $i < 2; ++$i)
  for ($j = 0; $j < sizeof($rest_aux); ++$j)
    $fin[] = $arr[0][$i].$rest_aux[$j];

}

return $fin;
}

$ar[0][0] = "R";
$ar[0][1] = "r";
$ar[1][0] = "S";
$ar[1][1] = "s";
$ar[2][0] = "T";
$ar[2][1] = "t";

$a = rest($ar);
reset ($a);
while (list($k, $v) = each ($a))
echo "($k) - $v<br>";

?>

Christian

[Anon]

The '#' are to preserve indentation.

$size=count($char);

$productsize=1<<$size;

for($j=0; $j<$size; ++$j)

{ $shift = $size-1-$j;

for($i=0; $i<$productsize; ++$i)

{ $k=($i>>$shift)&1;

$product[$i][$j]=$char[$j][$k];

}

}

Or if all your arrays are 1-indexed as per your example, instead of
the more common 0-indexing (note the changes to $shift and $k:

$size=count($char);

$productsize=1<<$size;

for($j=1; $j<=$size; ++$j)

{ $shift = $size-$j;

for($i=1; $i<=$productsize; ++$i)

{ $k=(($i-1)>>$shift)&1+1;

$product[$i][$j]=$char[$j][$k];

}

}

The results in $product are in the same format as $char (an array of arrays of characters)

[Anon]

Huh. The indentation didn't work. Oh, well.

[Anon]

Thanks a lot. You guys rule!