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<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width">
  <title>JS Bin</title>
</head>
<body>

<script id="jsbin-javascript">
'use strict';

var getBalancedLength = function getBalancedLength(str) {
  if (typeof str !== 'string') {
    console.error('Invalid type string.');
  }

  var token_queue = [];
  var res = [];

  var count = 0;

  var _iteratorNormalCompletion = true;
  var _didIteratorError = false;
  var _iteratorError = undefined;

  try {
    for (var _iterator = str[Symbol.iterator](), _step; !(_iteratorNormalCompletion = (_step = _iterator.next()).done); _iteratorNormalCompletion = true) {
      char = _step.value;

      if (/\(/.test(char)) token_queue.push(1);else if (/\)/.test(char)) {
        if (token_queue.length) {
          token_queue.shift();
          count += 2;
        } else {
          res.push(count);
          count = 0;
        }
      } else {
        console.error('Invalid type string.');
        break;
      }
    }
  } catch (err) {
    _didIteratorError = true;
    _iteratorError = err;
  } finally {
    try {
      if (!_iteratorNormalCompletion && _iterator['return']) {
        _iterator['return']();
      }
    } finally {
      if (_didIteratorError) {
        throw _iteratorError;
      }
    }
  }

  res.push(count);

  return Math.max.apply(Math, res);
};

console.clear();

console.log(getBalancedLength(''));
console.log(getBalancedLength('(a)'));
console.log(getBalancedLength(')('));
console.log(getBalancedLength('()'));
console.log(getBalancedLength('))(()()))'));
console.log(getBalancedLength('()())()((()))'));
</script>


<script id="jsbin-source-javascript" type="text/javascript">const getBalancedLength = (str) => {
  if(typeof str !== 'string') {
    console.error('Invalid type string.');
  }

  const token_queue = [];
  const res = [];

  let count = 0;

  for(char of str) {

    if(/\(/.test(char))
      token_queue.push(1);

    else if(/\)/.test(char)) {
      if(token_queue.length) {
        token_queue.shift();
        count += 2;
      } else {
        res.push(count);
        count = 0;
      }
    } else {
      console.error('Invalid type string.');
      break;
    }
  }

  res.push(count);

  return Math.max(...res);
}

console.clear();

console.log(getBalancedLength(''));
console.log(getBalancedLength('(a)'));
console.log(getBalancedLength(')('));
console.log(getBalancedLength('()'));
console.log(getBalancedLength('))(()()))'));
console.log(getBalancedLength('()())()((()))'));
</script></body>
</html>