Balanced parenthesis

balanced_parenthesis.js

function isBalanced(string) {
  var closers = {
    '{' : '}',
    '(' : ')',
    '[' : ']'
  }
  var stack = [];
  for (var i = 0, l = string.length; i < l; i++) {
      if (closers[string[i]]) {
          stack.push(string[i]);
      } else {
        if (closers[stack.pop()] !== string[i]) {
          return false;
        }
      }
  }
  return stack.length === 0;
}

balanced_parenthesis.py

# Check a string for balanced parenthesis

def is_balanced(string):
  if len(string) % 2:
    return False

  closers = {
    '(' : ')',
    '{' : '}',
    '[' : ']'
  }

  opened = []
  for ch in string:
    is_opener = closers.get(ch)
    if is_opener:
      opened.append(ch)
    else:
      if closers.get(opened.pop()) != ch:
        return False

  return True

if __name__ == '__main__':
  import unittest

  class TestIsBalanced(unittest.TestCase):

    def test_balanced(self):
      self.assertTrue(is_balanced('()'))
      self.assertTrue(is_balanced('{()}[]'))
      self.assertTrue(is_balanced('[({})]'))
      self.assertTrue(is_balanced('(())'))

    def test_unbalanced(self):
      self.assertFalse(is_balanced('('))
      self.assertFalse(is_balanced('[(])'))
      self.assertFalse(is_balanced('[{]}'))

  unittest.main()