Use a stack to check whether the parentheses in a string is balanced ()[]{}

balanced_parentheses.php

<?php
function is_pair($open, $close)
{
    if($open == '(' && $close == ')') return true;
    elseif($open == '{' && $close == '}') return true;
    elseif($open == '[' && $close == ']') return true;
    return false;
}
function balance($test)
{
    $stack = array();
    for($i = 0; $i < strlen($test); $i++)
    {
        $char = $test[$i];
        if(in_array($char, array('(', '[', '{')))
        {
            array_push($stack, $char);
        }
        elseif(in_array($char, array(')', ']', '}')))
        {
            if(empty($stack) || !is_pair(end($stack), $char))
            {
                return false;
            }
            else
            {
                array_pop($stack);
            }
        }
    }

    return empty($stack) ? true : false;
}

$tests = array('[{()}]', '[{([)}]', '[{]', '[]', '[', ']', '[{(}]', '([][]){}');

foreach($tests as $test)
{
    echo $test.' - ';
    if(balance($test))
        echo 'true';
    else
        echo 'false';
    echo "\n";
}