Very fast permutations in PHP - php

Question

I have searched the internet in great detail and found many samples of PHP scripts that are addressing permutations. All these scripts are ok for permuting a few numbers and a few words here and there but when we get to perform some heavy stuff I can't execute the code.
Here is the essence of the thing we need and things I did.
I have to find all unique combinations of a range of numbers from 1 to 8.
I do this easily,, no problems there...
Then I have to permute each combination which should result with a crazy number results,, and then I have to perform string replacements on each result...
I know this is intense,,, and I do manage to get it done with numbers up to 6.
6 Executes pretty slow,, and 7 and 8 simply mess with the memory allocation on the machine.
My primary question is
Is there a way I can do permutations super fast? Preferably without affecting memory too badly... AND how fast can in PHP realistically a few million records be displayed (doing it in command line,,, browser doesn't matter here)

Answer 1

I don't know if this will be helpful, but i already made a script that generates the permutation of 10 numbers (0 -> 9) in lexicographic order, and it runs in ~60sec [Quadcore 2.7Ghz] and uses 512MB due to the array sizes ...
By mathematical calculations: 10! = 3628800 permutations in 60 sec, 8! = 40320 permutations, so it should run in (60 * 40320) / 3628800 = 0.67sec say 1 second !
You may need to change the code for a 8-number permutations!
PS: I don't know if the browser would handel the output of +3M numbers !
<?php
/* 0 - > 9 PERMUTATION SCRIPT */
ini_set('memory_limit', '512M');
ini_set('max_execution_time', '0');
$st = timer();
$permutations = array();
for($a=0;$a<=9;$a++){
for($b=0;$b<=9;$b++){
if($b != $a){
for($c=0;$c<=9;$c++){
if($c != $a && $c != $b){
for($d=0;$d<=9;$d++){
if($d != $a && $d != $b && $d != $c){
for($e=0;$e<=9;$e++){
if($e != $a && $e != $b && $e != $c && $e != $d){
for($f=0;$f<=9;$f++){
if($f != $a && $f != $b && $f != $c && $f != $d && $f != $e){
for($g=0;$g<=9;$g++){
if($g != $a && $g != $b && $g != $c && $g != $d && $g != $e && $g != $f){
for($h=0;$h<=9;$h++){
if($h != $a && $h != $b && $h != $c && $h != $d && $h != $e && $h != $f && $h != $g){
for($i=0;$i<=9;$i++){
if($i != $a && $i != $b && $i != $c && $i != $d && $i != $e && $i != $f && $i != $g && $i != $h){
for($j=0;$j<=9;$j++){
if($j != $a && $j != $b && $j != $c && $j != $d && $j != $e && $j != $f && $j != $g && $j != $h && $j != $i){
$permutations[] = $a.$b.$c.$d.$e.$f.$g.$h.$i.$j;
}
}
}
}
}
}
}
}
}
}
}
}
}
}
}
}
}
}
}
echo count($permutations);
$et = timer();
$time = $et - $st;
echo "<br/>in : ".$time." seconds.";
function timer(){
list($usec, $sec) = explode(" ", microtime());
return((float)$usec + (float)$sec);
}
?>
EDIT: 1->8 permutation script in: ~0.43 seconds.
<?php
$permutations = array();
for($a=1;$a<=8;$a++){
for($b=1;$b<=8;$b++){
if($b != $a){
for($c=1;$c<=8;$c++){
if($c != $a && $c != $b){
for($d=1;$d<=8;$d++){
if($d != $a && $d != $b && $d != $c){
for($e=1;$e<=8;$e++){
if($e != $a && $e != $b && $e != $c && $e != $d){
for($f=1;$f<=8;$f++){
if($f != $a && $f != $b && $f != $c && $f != $d && $f != $e){
for($g=1;$g<=8;$g++){
if($g != $a && $g != $b && $g != $c && $g != $d && $g != $e && $g != $f){
for($h=1;$h<=8;$h++){
if($h != $a && $h != $b && $h != $c && $h != $d && $h != $e && $h != $f && $h != $g){
$permutations[] = $a.$b.$c.$d.$e.$f.$g.$h;
}
}
}
}
}
}
}
}
}
}
}
}
}
}
}
echo count($permutations);
?>