Task with nested string

gistfile1.rb

=begin
A string S consisting of N characters is called properly nested if:

        S is empty;
        S has the form "(U)" where U is a properly nested string;
        S has the form "VW"

where V and W are properly nested strings.

For example, string "(()(())())" is properly nested but string "())" isn't.

Write a function

    def nesting(s) 

that, given a string S consisting of N characters, returns 1 if string S is properly nested and 0 otherwise.

Assume that:

        N is an integer within the range [0..1,000,000];
        string S consists only of the characters ( and/or ).

For example, given S = "(()(())())", the function should return 1 and given S = "())", the function should return 0, as explained above.

Complexity:

        expected worst-case time complexity is O(N);
        expected worst-case space complexity is O(1) (not counting the storage required for input arguments).
=end

def nesting(str)
  size = str.size
  return 1 if size == 0
  # открытая скобка прибавляет к счетчику 1, закрытая уменьшает на 1
  # если в итоге получилось 0 - properly nested
  open_bracket_counter = 0
  for i in 0..size-1 do
    open_bracket_counter += 1 if str[i] == '('
    open_bracket_counter -= 1 if str[i] == ')'
    # если первая скобка ')', значит счетчик уйдёт в минус и нам все ясно
    return 0 if open_bracket_counter == -1
  end
  return open_bracket_counter == 0 ? 1 : 0
end

puts nesting('()h(el)() (( () )) (()) ()((( (()()()())))) lo')