polishcalculator.php

<?php

class polishcalculator {

  /**
   * Variables
   */
	private $expected;
	private $polishexprestion;
	private $token;
	private $result;
	private $isValid;
	private $stack;
	
	public function __construct($postfixpolish) {
		$this->polishexprestion = $postfixpolish;
	}
	
	/**
   * Evaluation function
   */
	public function evaluate() {
		$this->result = 0;
		$this->isValid = false;
		
		//validate
		$this->isValid = $this->isExpressionValid();
		
		if( $this->isValid ) {
			//split expression
			$this->token = $this->splitexpression();
			
			//store in stack
			$this->result = $this->storeInStackAndCalc();
		}
		return (int)$this->result;
	}

	/**
   * Expression validation
   */
	public function isExpressionValid() {
		
		// is empty
		$isValidArr[] = ( isset($this->polishexprestion) && empty($this->polishexprestion) ) ? false : true;
		
		// check string via regex, allow numbers and operators only
		preg_match("/^[0-9 \+\*\/\-\^\%]+$/", $this->polishexprestion, $output_array);
		$isValidArr[] = ( isset($output_array) && !is_array($output_array) && count($output_array) == 0 ) ? false : true;
		
		return ( in_array( false, $isValidArr ) ) ? false : true;
	}
	
	/**
   * Split expression by space
   */
	public function splitexpression() {
		return preg_split('/[\s]+/', trim($this->polishexprestion));
	}
	
	/**
   * Store the tokens in stack and calculate the expressions
   */
	public function storeInStackAndCalc() {
		$this->stack = Array();
		
		foreach ( $this->token as $token ) {
			if( preg_match("/^[\+\*\/\-\^\%]+$/", $token ) === 0 ) {
				// IF NO OPERATORS THEN PUSH TO STACK
				array_push($this->stack, $token);			
			} else {
				// IF OPERATOR THEN POP AND CALCULATE
				$firstNumber = $secondNumber = 0;
				
				$operator = $token;
				
				if( $operator !== '%' ) {
					// DO NOT POP EXTRA ELEMENT IN CASE OF % AS IN OUR CASE IT IS UNARY OPERATOR
					$secondNumber = array_pop($this->stack);
				}
				$firstNumber = array_pop($this->stack);
				
				if( $operator == '^' ) {
					// POWER
					$pushtostack = pow($firstNumber,$secondNumber);
				} else if( $operator == '%' ) {
					// PERCENTAGE
					$pushtostack = $firstNumber / 100;
				} else {
					// ADD, SUB, MUL, DIV
					$expression = $firstNumber . $operator . $secondNumber;
					$pushtostack = eval('return '.$expression.';');
				}
				
				// Push the calculated result to stack
				array_push($this->stack, $pushtostack );
			}
		}
		return array_pop($this->stack);
	}
}
// EOF :)
?>