Validate a string for matching opening and closing parentheses and brackets.

validate_matching_parentheses

# create a stack
# set the lookup hash
# set left = lookup.keys
# set right = lookup.values

# for each char in string
  # is it a left bracket?
    # add character on the stack
  # if not, is it a right bracket?
    # pop the last left bracket from the stack
    # does it match to the current character? (right bracket)
      # if it doesn't return false
    # is the stack empty?
      # return false

# is the stack empty?
  # return true or false 
  
  
def smarter_validate(str)
  stack  = []
  lookup = { '(' => ')', '[' => ']', '{' => '}', '<' => '>' }
  left   = lookup.keys
  right  = lookup.values

  str.each_char do |char|
    if left.include? char
      stack << char
    elsif right.include? char
      return false if stack.empty? || (lookup[stack.pop] != char)
    end
  end

  return stack.empty?
end