PHP Number Game Calculate 24 Algorithm

Algorithm idea: Treat each number as an independent mathematical expression. Add punctuation marks between the expressions to form a new expression. A total of 4 combinations. All combinations between expressions can be achieved through recursion.
The code is as follows:

. The code is as follows:

/** 
* A 24 maker 
* @version 1.0.0 
* @author laruence 
* @copyright (c) 2009 http://www.laruence.com 
*/
class TwentyFourCal {
public $needle = 24;
public $precision = '1e-6';
function TwentyFourCal() {
}
private function notice($mesg) {
var_dump($mesg);
}
/**
* Get user input method
*/
public function calculate($operants = array()) {
try {
$this->search($operants, 4);
} catch (Exception $e) {
$this->notice($e->getMessage());
return;
}
$this-> ;notice('can't compute!');
return;
}
/**
* Looking for PHP implementation of 24-point algorithm
*/
private function search($expressions, $level) {
if ($level == 1) {
$ result = 'return ' . $expressions[0] . ';';
if ( abs(eval($result) - $this->needle) <= $this->precision) {
throw new Exception( $expressions[0]);
}
}
for ($i=0;$i<$level;$i++) {
for ($j=$i+1;$j<$level;$j++) {
$expLeft = $expressions[$i];
$expRight = $expressions[$j];
$expressions[$j] ​​= $expressions[$level - 1];
$expressions[$i] = '(' . $expLeft . ' + ' . $expRight . ')';
$this->search($expressions, $level - 1);
$expressions[$i] = '(' . $expLeft . ' * ' . $expRight . ')';
$this->search($expressions, $level - 1);
$expressions[$i] = '(' . $expLeft . ' - ' . $expRight . ')' ;
$this->search($expressions, $level - 1);
$expressions[$i] = '(' . $expRight . ' - ' . $expLeft . ')';
$this-> search($expressions, $level - 1);
if ($expLeft != 0) {
$expressions[$i] = '(' . $expRight . ' / ' . $expLeft . ')';
$this ->search($expressions, $level - 1);
}
if ($expRight != 0) {
$expressions[$i] = '(' . $expLeft . ' / ' . $expRight . ') ';
$this->search($expressions, $level - 1);
}
$expressions[$i] = $expLeft;
$expressions[$j] ​​= $expRight;
}
}
return false ;
}
function __destruct() {
}
}
/* demo */
$tf = new TwentyFourCal();
$tf->calculate( array(4,8,8,8) );
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