求: 三个5,一个1组成的数学表达式的结果=24,   结果:(5-1/5)*5=24

<?php

 set_time_limit(0);
 $values = array(1, 5, 5, 5);
 $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;
 }

?>