Simple stack in Ruby

stack.rb

# Author: Ivan E. Cao-Berg ([email protected])
#
# Copyright (C) 2012-2025
# School of Computer Science
# Carnegie Mellon University
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published
# by the Free Software Foundation; either version 2 of the License,
# or (at your option) any later version.
#
# This program is distributed in the hope that it will be useful, but
# WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
# General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
# 02110-1301, USA.
#
# For additional information visit http://www.andrew.cmu.edu/~icaoberg or
# send email to [email protected]

class Stack
  def initialize
    @stack = []
  end

  # Adds a value to the stack
  # @param value [Object] the value to be added
  # @return [Boolean] true if the value is successfully added, false otherwise
  def push(value)
    return false if value.nil?

    @stack.unshift(value)
    true
  end

  # Returns the top value of the stack without removing it
  # @return [Object, nil] the top value of the stack or nil if the stack is empty
  def peek
    @stack.first
  end

  # Removes the top value from the stack
  # @return [Boolean] true if a value was removed, false otherwise
  def pop
    [email protected]?
  end

  # Returns the number of elements in the stack
  # @return [Integer] the size of the stack
  def size
    @stack.length
  end

  # Checks if the stack contains a specific value
  # @param value [Object] the value to check for
  # @return [Boolean] true if the value exists, false otherwise
  def contains?(value)
    @stack.include?(value)
  end

  # Clears all elements from the stack
  def clear
    @stack.clear
  end

  # Checks if the stack is empty
  # @return [Boolean] true if the stack is empty, false otherwise
  def empty?
    @stack.empty?
  end
end