一個強悍的算24點游戲的PHP程序(遞歸函數的妙用)

研究遞歸函數 找到的一個經典的例子

<?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; 
}
?></pre>原文地址：http://www.nowamagic.net/php/php_24PointsGame.php