朋友問了一個關於逆波蘭式的問題.
程式不好.用了 Interpreter 設計模式參上了
記錄一下.
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| <?php
interface Expression {
public function interpret(array $s);
}
class ExperssionNumber implements Expression {
private $number;
public function __construct($number) {
$this->number = $number;
}
public function interpret(array $s) {
array_push($s, $this->number);
}
}
class ExperssionPlus implements Expression {
public function interpret(array $s) {
array_push($s, array_pop($s) + array_pop($s));
}
}
class ExpressionMinus implements Expression {
public function interpret(array $s) {
array_push($s, - array_pop($s) + array_pop($s));
}
}
class Parser {
private $parse_tree = array();
public function __construct($s) {
foreach(explode(" ", $s) as $token) {
switch($token) {
case "+": array_push($this->parse_tree, new ExperssionPlus()); break;
case "-": array_push($this->parse_tree, new ExpressionMinus()); break;
default: array_push($this->parse_tree, new ExperssionNumber($token)); break;
}
}
}
public function evaluate() {
$context = array();
foreach($this->parse_tree as $expression) {
$expression->interpret(&$context);
}
return array_pop($context);
}
}
class Test {
public static function run($experssion) {
($parser = new Parser($experssion)) && print($parser->evaluate()."\n");
}
}
Test::run("100 32 25 - +");
?>
|
