PHP使用逆波兰式计算工资的方法

<?php
/**
 * math_rpn 
 *
 * 实现逆波兰式算法
 *  
 */
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*/