function filterEquationBrackets($q)
{
$serializedEquation = serializeEquationToArray($q);
$equation = deserializeArrayToEquation($serializedEquation);
$filteredSerializedEquation = filterBracketBySerializedEquation($serializedEquation);
return deserializeArrayToEquation($filteredSerializedEquation);
}
function filterBracketBySerializedEquation($serializedEquation, $prevOperator = null, $nextOperator = null)
{
if (!is_array($serializedEquation)) {
return $serializedEquation;
}
foreach ($serializedEquation as $key => &$subEquation) {
// skip if not array
if (!is_array($subEquation)) {
continue;
}
// get previous and next operator
$prevOperator = isset($serializedEquation[$key - 1]) ? $serializedEquation[$key - 1] : $prevOperator;
$nextOperator = isset($serializedEquation[$key + 1]) ? $serializedEquation[$key + 1] : $nextOperator;
// set is remove bracket flag
$isRemoveBracket = true;
foreach ($subEquation as $subKey => $c) {
// if not operator, skip
if (!in_array($c, array('+', '-', '*', '/'))) {
continue;
}
// case by case, for +, -, *, /
switch ($c) {
case '+':
case '-':
if (in_array($prevOperator, array('-', '*', '/')) || in_array($nextOperator, array('*', '/'))) {
$isRemoveBracket = false;
}
break;
case '*':
case '/':
if ($prevOperator == '/') {
$isRemoveBracket = false;
}
break;
default:
break;
}
}
// remove unnecessary brackets
if ($isRemoveBracket) {
array_shift($subEquation);
array_pop($subEquation);
}
// recursive filter unnecessary brackets
$subEquation = filterBracketBySerializedEquation($subEquation, $prevOperator, $nextOperator);
}
unset($subEquation);
return $serializedEquation;
}
