Ruby Bracket Validator

original_bracket_validator.rb

require 'set'

def is_valid(code)
    openers_to_closers = {
        '(' => ')',
        '{' => '}',
        '[' => ']'
    }

    openers = Set.new(openers_to_closers.keys.to_set)
    closers = Set.new(openers_to_closers.values.to_set)

    openers_stack = []

    for i in 0...code.length
        char = code[i]
        if openers.include? char
            openers_stack.push(char)
        elsif closers.include? char
            if openers_stack.empty?
                return false
            else
                last_unclosed_opener = openers_stack.pop

                # if this closer doesn't correspond to the most recently
                # seen unclosed opener, short-circuit, returning false
                if openers_to_closers[last_unclosed_opener] != char
                    return false
                end
            end
        end
    end
    return openers_stack == []
end

updated_bracket_validator.rb

require 'set'

# 2-space indents conventional in Ruby

# Predicate methods conventionally end with a question mark
# (often without a is_/has_-prefix).
def valid?(code)
  openers_to_closers = {
    '(' => ')',
    '{' => '}',
    '[' => ']'
  }

  openers = openers_to_closers.keys.to_set
  closers = openers_to_closers.values.to_set

  openers_stack = []

  # Conventionally each is favored over for loops (thought to be a readability improvement)
  code.chars.each do |char|
    if openers.include? char
      openers_stack.push(char)
    elsif closers.include? char
      return false if openers_stack.empty?

      last_unclosed_opener = openers_stack.pop

      # if this closer doesn't correspond to the most recently
      # seen unclosed opener, short-circuit, returning false
      return false if openers_to_closers[last_unclosed_opener] != char
    end
  end
  openers_stack.empty?
end