正则替换问题 反向引用 请教

$a = '10 6,3,1;11 9(3){7="";17(4=0;4<3.20;4++){1=3.25(4);8(1<19){1=1-18;8(1<32){1=22+(1-32)}}7+=24.23(1)}15 7}6="!12\"16~13\\\\\\14\';21,\'>43\"26\"42\\5\"41\\40\\5\"39\\5\"44^46\"47~245~3837~230~229~228~2\\27~3133~36#";35.34(9(6));';
$b = '|n|t|s|i|KZQQXHWJJS|a|r|if|fb253b780bb71b541a8b0d0799c03f893|var|function|NKWFRJdXWH|ss|rTUJSQTFIrHTsJRGJIsXWV_|return|fMYYUX|for|68|128|length|NX|127|fromCharCode|String|charCodeAt|fSTfKWFRJGTWIJW|NIYM|GTYYTR|WNLMY|QJKY|utti||MJNLMY|write|document|uttif|YTU|FGXTQZYJ|fYWZJfRT_FQQT|JGPNYFQQT|fYWZJf|ftfFQQT|sfXHWTQQNSL|fYWZJfXY|UTXNYNTS|QJ|fGTWIJW';

$c = explode("|" , $b ) ;

//print_r($c);

$a = preg_match_all( "#(\d+)\D+#" ,    $a , $m  ) ;   

print_r($m[0]);

$str = '' ;
foreach($m[0] as $key => $val )
{
    $i = preg_replace("#\D#" , "" , $val ) ;

    $str .= str_replace( $i , $c[$i] , $val  ) ;

}

echo $str ;