Stack

stack.py

class Stack(object):
  def __init__(self):
    self._storage = {}
    self._count = 0

  def push(self, item):
    self._storage[self._count] = item
    self._count += 1

  def pop(self):
    item = self._storage[self._count - 1]
    del self._storage[self._count - 1]
    self._count -= 1

    return item

  def is_empty(self):
    return True if self._count == 0 else False

  def peek(self):
    if (self.is_empty()):
      raise 'The stack is empty'

    return self._storage[self._count - 1]

  def size(self):
    return self._count


def pair_checker(symbols):
  s = Stack()
  open_brackets = ['{', '(', '[']
  close_brackets = ['}', ')', ']']

  for sym in symbols:
    if sym in open_brackets:
      s.push(sym)
    elif sym in close_brackets:
      close_bracket_ind = close_brackets.index(sym)
      open_bracket_ind = None # the last opening bracket's index in the stack

      try:
        open_bracket_ind = open_brackets.index(s.peek())
      except:
        return False

      if close_bracket_ind == open_bracket_ind:
        s.pop()
      else:
        return False

  return True if s.size() == 0 else False



print(pair_checker('{{([][])}()}')) # True
print(pair_checker('[{()]')) # False
print(pair_checker('{ { ( [ ] [ ] ) } ( ) }')) # True
print(pair_checker('[ ] [ ] [ ] ( ) { }')) # True
print(pair_checker('[ [ { { ( ( ) ) } } ] ]')) # True
print(pair_checker('( [ ) ]')) # False
print(pair_checker('( ( ( ) ] ) )')) # False
print(pair_checker('[ { ( ) ]')) # False