一个强悍的算24点游戏的PHP程序(递归函数的妙用)

研究递归函数 找到的一个经典的例子

<?php    set_time_limit(0);   $values = array(5, 5, 5, 1);   $result = 24;    $list = array();    echo "<pre>";   makeValue($values);   print_r($list);    function makeValue($values, $set=array())   {    $words = array("+", "-", "*", "/");    if(sizeof($values)==1)    {     $set[] = array_shift($values);     return makeSpecial($set);    }       foreach($values as $key=>$value)    {     $tmpValues = $values;     unset($tmpValues[$key]);     foreach($words as $word)     {      makeValue($tmpValues, array_merge($set, array($value, $word)));     }    }   }     function makeSpecial($set)   {    $size = sizeof($set);     if($size<=3 || !in_array("/", $set) && !in_array("*", $set))    {     return makeResult($set);    }     for($len=3; $len<$size-1; $len+=2)    {     for($start=0; $start<$size-1; $start+=2)     {      if(!($set[$start-1]=="*" || $set[$start-1]=="/" || $set[$start+$len]=="*" || $set[$start+$len]=="/"))       continue;      $subSet = array_slice($set, $start, $len);      if(!in_array("+", $subSet) && !in_array("-", $subSet))       continue;      $tmpSet = $set;      array_splice($tmpSet, $start, $len-1);      $tmpSet[$start] = "(".implode("", $subSet).")";      makeSpecial($tmpSet);     }    }   }    function makeResult($set)   {    global $result, $list;    $str = implode("", $set);    @eval("\$num=$str;");    if($num==$result && !in_array($str, $list))    $list[] = $str;   }    ?>