<?php
// Returns the total number of $count-length strings generatable from $letters.
function getPermCount($letters, $count)
{
$result = 1;
// k characters from a set of n has n!/(n-k)! possible combinations
for($i = strlen($letters) - $count + 1; $i <= strlen($letters); $i++) {
$result *= $i;
}
return $result;
}
// Decodes $index to a $count-length string from $letters, no repeat chars.
function getPerm($letters, $count, $index)
{
$result = '';
for($i = 0; $i < $count; $i++)
{
$pos = $index % strlen($letters);
$result .= $letters[$pos];
$index = ($index-$pos)/strlen($letters);
$letters = substr($letters, 0, $pos) . substr($letters, $pos+1);
}
return $result;
}
$letters = 'abc';
$r = array();
//echo '1 letters from 4: ';
for($i = 0; $i < getPermCount($letters, 1); $i++)
$r[] = getPerm($letters, 1, $i);
//echo '2 letters from 4: ';
for($i = 0; $i < getPermCount($letters, 2); $i++)
$r[] = getPerm($letters, 2, $i);
//echo ' 3 letters from 4: ';
for($i = 0; $i < getPermCount($letters, 3); $i++)
$r[] = getPerm($letters, 3, $i);
print_r($r);
preferences:
37.89 ms | 402 KiB | 5 Q