Parentheses Validator

parentheses_validator.php

// Function that tells us whether or not an input string's openers and closers are properly nested.
// Examples:
// • "{ [ ] ( ) }" should return True
// • "{ [ ( ] ) }" should return False
// • "{ [ }" should return False


function parentheses_validatior($string){

    // remove spaces
    $string = str_replace(' ', '', $string);

    // turn string into array of chars
    $arr_char = str_split($string);

    if(count($arr_char)%2 == 1)
        return FALSE;

    $opening_brackets = [];

    foreach($arr_char as $char){

        if(in_array($char, array("{", "(", "["))===TRUE)
            $opening_brackets[] = $char;

        else if(in_array($char, array("}", ")", "]"))===TRUE){

            $last_idx = count($opening_brackets)-1;

            if($char == "}" && $opening_brackets[$last_idx] == "{")
                array_pop($opening_brackets);
            
            else if($char == "]" && $opening_brackets[$last_idx] == "[")
                array_pop($opening_brackets);

            else if($char == ")" && $opening_brackets[$last_idx] == "(")
                array_pop($opening_brackets);
        }
    }

    if(count($opening_brackets) == 0)
        return TRUE;
    else 
        return FALSE;
}

$validator1 = parentheses_validatior("{ [ ] ( ) }");    // TRUE
var_dump($validator1);

$validator2 = parentheses_validatior("{ [ ( ] ) }");    // FALSE
var_dump($validator2);

$validator3 = parentheses_validatior("{ [ }");    // FALSE
var_dump($validator3);

$validator4 = parentheses_validatior("{ [{[{}[]{}]}] {} }");    // TRUE
var_dump($validator4);