Reverse Polish Notation

rpn.php

<?php

// some tests to run
$tests[] = array(2, 1, '+', 3, '*');
$tests[] = array(4, 10, 5, '/', '+');
$tests[] = array(4, 13, 5, '/', '+');
$tests[] = array(4, 2, 5, '*', '+', 1, 3, 2, '*', '+', '/');

// expected resuluts
$expected = array(9, 6, 6.6, 2);

/**
 * reverse Polish notation
 *
 * @param array $array input array
 *
 * @return int;
 */
function rpn($array) {

	// init some variables
	$numbers = array();
	$return = $num1 = $num2 = 0;

	// loop thru all elements

	for ($a = 0, $max = count($array); $a < $max; $a++) {

		// check if current element is number, and put it on stack
		if (is_numeric($array[$a])) {
			$numbers[] = $array[$a];
		} else {

			// get numbers from stack
			$num1 = array_pop($numbers);
			$num2 = array_pop($numbers);

			// make operation
			switch ($array[$a]) {
				case '+':
					$return = $num2 + $num1;
					break;
				case '-':
					$return = $num2 - $num1;
					break;
				case '/':
					$return = $num2 / $num1;
					break;
				case '*':
					$return = $num2 * $num1;
					break;
			}

			// push result on stack
			array_push($numbers, $return);
		}
	}
	return $return;
}

// loop thru samples
for ($a = 0, $max = count($tests); $a < $max; $a++) {

	$result = rpn($tests[$a]);
	
    if ($result !== $expected[$a]) {
		echo "failed got {$result} expected {$expected[$a]}";
	} else {
		echo 'passed!';
	}
	echo "\n";
}