24点递归算法PHP版本

[Meteorlet]

<?php
function Calculate24Point($a, &$r, &$ex, $n)
{
    $ex2 = $ex;
    if($n == 1)
    {
        if( abs($a[0] - 24) <= 0.000001 )
        {
            $r[] = $ex[0];
            return true;
        } else {
            return false;
        }
    }
    for($i = 0; $i < $n; $i ++)
    {
        for($j = $i + 1; $j < $n; $j ++)
        {
            $x = $a[$i];
            $y = $a[$j];
            $a[$j] = $a[$n - 1];

            $exa = $ex[$i];
            $exb = $ex[$j];
            $ex[$j] = $ex[$n - 1];

            $a[$i] = $x + $y;
            $ex[$i] = "($exa + $exb)";
            if(Calculate24Point($a, $r, $ex, $n - 1))
            {
                return true;
            }

            $a[$i] = $x - $y;
            $ex[$i] = "($exa - $exb)";
            if(Calculate24Point($a, $r, $ex, $n - 1))
            {
                return true;
            }

            $a[$i] = $y - $x;
            $ex[$i] = "($exb - $exa)";
            if(Calculate24Point($a, $r, $ex, $n - 1))
            {
                return true;
            }

            $a[$i] = $x * $y;
            $ex[$i] = "($exa * $exb)";
            if(Calculate24Point($a, $r, $ex, $n - 1))
            {
                return true;
            }

            if($y != 0)
            {
                $a[$i] = $x / $y;
                $ex[$i] = "($exa / $exb)";
                if(Calculate24Point($a, $r, $ex, $n - 1))
                {
                    return true;
                }
            }

            if($x != 0)
            {
                $a[$i] = $y / $x;
                $ex[$i] = "($exb / $exa)";
                if(Calculate24Point($a, $r, $ex, $n - 1))
                {
                    return true;
                }
            }
            $a[$i] = $x;
            $a[$j] = $y;
            $ex = $ex2;
        }
    }
    return false;
}

$a[0] = $ex[0] = $_REQUEST['a1'];
$a[1] = $ex[1] = $_REQUEST['a2'];
$a[2] = $ex[2] = $_REQUEST['a3'];
$a[3] = $ex[3] = $_REQUEST['a4'];

if(Calculate24Point($a, $result, $ex, count($a)))
{
    for($i = 0; $i < count($result); $i ++)
    {
        echo "Answer: " . $result[$i] . "<br>\r\n";
    }
} else {
    echo "No Answer.";
}
?>

<form action="" method="POST">
<input type="text" size="8" name="a1" value="<?php echo $_REQUEST['a1'];?>"/>
<input type="text" size="8" name="a2" value="<?php echo $_REQUEST['a2'];?>"/>
<input type="text" size="8" name="a3" value="<?php echo $_REQUEST['a3'];?>"/>
<input type="text" size="8" name="a4" value="<?php echo $_REQUEST['a4'];?>"/>
<input type="submit" value="Calculate"/>
</form>

之前有人问起过，递归算法供大家参考。

[SysTem128]

看起来是改C的,看过这个.

http://topic.csdn.net/u/20071118/18/0c126923-08b0-44d5-a75c-7f79a6fe8c9b.html