Fsm Simulator from Udacity CS262 implemented in ruby...

fsmsim.rb

# FSM Simulation

edges = {
  [1, 'a'] => 2,
  [2, 'a'] => 2,
  [2, '1'] => 3,
  [3, '1'] => 3
}

accepting = [3]

def fsmsim string, current, edges, accepting
  if string == ""
    return accepting.include? current
  else
    char = string[0]
    if edges.key? [current, char]
      remaining_string = string[1..-1]
      destination = edges.fetch [current, char]
      return fsmsim remaining_string, destination, edges, accepting
    else
      return false
    end
  end
end

puts fsmsim("aaa111", 1, edges, accepting)
puts fsmsim("a1a1a1", 1, edges, accepting)
puts fsmsim("a1", 1, edges, accepting)


# edges = {(1, 'a') : 2,
# (2, 'a') : 2,
# (2, '1') : 3,
# (3, '1') : 3}

# accepting = [3]

# def fsmsim(string, current, edges, accepting):
#   if string == "":
#     return current in accepting
#   else:
#     letter = string[0]
#     # QUIZ: You fill this out!
#     # Is there a valid edge?
#     if (current, letter) in edges:
#       # If so, take it.
#       remaining_string = string[1:]
#       distination = edges[current, letter]
#       # Hint: recursion.
#       fsmsim(remaining_string, distination, edges, accepting)
#     else:
#       # If not, return False.
#       return false

# print fsmsim("aaa111",1,edges,accepting)
# >>> True