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<?php
/**
* Author: Alexander "NeonXP" Kiryukhin
* Date: 14.03.13
* Time: 1:01
*/
namespace NXP;
/**
* Class MathExecutor
* @package NXP
*/
class MathExecutor {
const LEFT_ASSOCIATED = 'LEFT_ASSOCIATED';
const RIGHT_ASSOCIATED = 'RIGHT_ASSOCIATED';
const NOT_ASSOCIATED = 'NOT_ASSOCIATED';
const UNARY = 'UNARY';
const BINARY = 'BINARY';
private $operators = [ ];
/**
* Base math operators
*/
public function __construct()
{
$this->addOperator('+', 1, function ($op1, $op2) { return $op1 + $op2; });
$this->addOperator('-', 1, function ($op1, $op2) { return $op1 - $op2; });
$this->addOperator('*', 2, function ($op1, $op2) { return $op1 * $op2; });
$this->addOperator('/', 2, function ($op1, $op2) { return $op1 / $op2; });
$this->addOperator('^', 3, function ($op1, $op2) { return pow($op1, $op2); });
}
/**
* Add custom operator
* @param string $name
* @param int $priority
* @param callable $callback
* @param string $association
* @param string $type
*/
public function addOperator($name, $priority, callable $callback, $association = self::LEFT_ASSOCIATED, $type = self::BINARY)
{
$this->operators[$name] = [
'priority' => $priority,
'association' => $association,
'type' => $type,
'callback' => $callback
];
}
/**
* Execute expression
* @param $expression
* @return int|float
*/
public function execute($expression)
{
$reversePolishNotation = $this->convertToReversePolishNotation($expression);
$result = $this->calculateReversePolishNotation($reversePolishNotation);
return $result;
}
/**
* Convert expression from normal expression form to RPN
* @param $expression
* @return array
* @throws \Exception
*/
protected function convertToReversePolishNotation($expression)
{
$stack = new \SplStack();
$queue = [];
$currentNumber = '';
for ($i = 0; $i < strlen($expression); $i++)
{
$char = substr($expression, $i, 1);
if (is_numeric($char) || (($char == '.') && (strpos($currentNumber, '.')===false))) {
$currentNumber .= $char;
} elseif ($currentNumber!='') {
$queue = $this->insertNumberToQueue($currentNumber, $queue);
$currentNumber = '';
}
if (array_key_exists($char, $this->operators)) {
while ($this->o1HasLowerPriority($char, $stack)) {
$queue[] = $stack->pop();
}
$stack->push($char);
}
if ($char == '(') {
$stack->push($char);
}
if ($char == ')') {
if ($currentNumber!='') {
$queue = $this->insertNumberToQueue($currentNumber, $queue);
$currentNumber = '';
}
while (($stackChar = $stack->pop()) != '(') {
$queue[] = $stackChar;
}
/**
* @TODO parse functions here
*/
}
}
if ($currentNumber!='') {
$queue = $this->insertNumberToQueue($currentNumber, $queue);
}
while (!$stack->isEmpty()) {
$queue[] = ($char = $stack->pop());
if (!array_key_exists($char, $this->operators)) {
throw new \Exception('Opening bracket has no closing bracket');
}
}
return $queue;
}
/**
* Calculate value of expression
* @param array $expression
* @return int|float
* @throws \Exception
*/
protected function calculateReversePolishNotation(array $expression)
{
$stack = new \SplStack();
foreach ($expression as $element) {
if (is_numeric($element)) {
$stack->push($element);
} elseif (array_key_exists($element, $this->operators)) {
$operator = $this->operators[$element];
switch ($operator['type']) {
case self::BINARY:
$op2 = $stack->pop();
$op1 = $stack->pop();
$operatorResult = $operator['callback']($op1, $op2);
break;
case self::UNARY:
$op = $stack->pop();
$operatorResult = $operator['callback']($op);
break;
default:
throw new \Exception('Incorrect type');
}
$stack->push($operatorResult);
}
}
$result = $stack->pop();
if (!$stack->isEmpty()) {
throw new \Exception('Incorrect expression');
}
return $result;
}
/**
* @param $char
* @param $stack
* @return bool
*/
private function o1HasLowerPriority($char, \SplStack $stack) {
if (($stack->isEmpty()) || ($stack->top() == '(')) {
return false;
}
$stackTopAssociation = $this->operators[$stack->top()]['association'];
$stackTopPriority = $this->operators[$stack->top()]['priority'];
$charPriority = $this->operators[$char]['priority'];
return
(($stackTopAssociation != self::LEFT_ASSOCIATED) && ($stackTopPriority > $charPriority)) ||
(($stackTopAssociation == self::LEFT_ASSOCIATED) && ($stackTopPriority >= $charPriority));
}
/**
* @param string $currentNumber
* @param array $queue
* @return array
*/
private function insertNumberToQueue($currentNumber, $queue)
{
if ($currentNumber[0]=='.') {
$currentNumber = '0'.$currentNumber;
}
$currentNumber = trim($currentNumber, '.');
$queue[] = $currentNumber;
return $queue;
}
}
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