My first Tail Recursive Ruby script

path_finder.rb

# Tail Recursive
# A to Z path finder

def path_finder(arr, n = nil)
  arr = arr.dup
  n ||= Array(arr.shift)
  val = arr.shift
  if n.last.last == val.first
    path_finder(arr, n << val)
  elsif arr.any? {|b| n.last.last == b.first}
    path_finder(arr.push(val), n)
  else
    n
  end
end

y = ["AB", "BC", "BZ", "DG", "AZ", "CG", "GZ", "DG", "DK", "AH", "EH"]

path_finder(y)
#  => ["AB", "BC", "CG", "GZ"] 

I really like your arr.dup unless n. And the use of tail is nice.

I wonder about possibly implementing more functionality with this method. For example all possible paths from A to Z, or shortest. Since "AZ" is one option that would be a simple test case to implement. But I wonder if that would be overkill for this.