PHP实现逆波兰式 - 计算工资时用

http://www.oschina.net/code/snippet_167160_6512

<?php
/**
 * math_rpn 
 *
 * 实现逆波兰式算法
 *   
 * @author   sparkHuang 260558820@qq.com
 * @version  RPN 1.0.0 
 * 
 */

class math_rpn {
    //初始的计算表达式
    private $_expression = '';
    //处理后的逆波兰表达式
    private $_rpnexp = array();
    
    //模拟栈结构的数组
    private $_stack  = array('#');
    
    //正则判断
    //private $_reg    = '/^([A-Za-z0-9\(\)\+\-\*\/])*$/';
    
    //优先级
    private $_priority = array('#' => 0, '(' => 10, '+' => 20, '-' => 20, '*' => 30, '/' => 30);
    
    //四则运算
    private $_operator = array('(', '+', '-', '*', '/', ')');
    
    public function __construct($expression) {
        $this->_init($expression);
    }
    
    private function _init($expression) {
        $this->_expression = $expression;
    }
    
    public function exp2rpn() {
        $len = strlen($this->_expression);
        
        for($i = 0; $i < $len; $i++) {
            $char = substr($this->_expression, $i, 1);
            
            if ($char == '(') {
                $this->_stack[] = $char;
                continue;
            } else if ( ! in_array($char, $this->_operator)) {
                $this->_rpnexp[] = $char;
                continue;
            } else if ($char == ')') {
                for($j = count($this->_stack); $j >= 0; $j--) {
                    $tmp = array_pop($this->_stack);
                    if ($tmp == "(") {
                        break;    
                    } else {
                        $this->_rpnexp[] = $tmp;
                    }
                }
                continue;
            } else if ($this->_priority[$char] <= $this->_priority[end($this->_stack)]) {
                $this->_rpnexp[] = array_pop($this->_stack);
                $this->_stack[]  = $char;
                continue;
            } else {
                $this->_stack[] = $char;
                continue;
            }
        }
        for($i = count($this->_stack); $i >= 0; $i--) {
            if (end($this->_stack) == '#') break;
            $this->_rpnexp[] = array_pop($this->_stack);    
        }
        return $this->_rpnexp;
    }
}

//测试实例
$expression = "(A*(B+C)-E+F)*G";
var_dump($expression);
$mathrpn = new math_rpn($expression);
var_dump($mathrpn->exp2rpn());

/*End of php*/