dirReduc.rb

HASH = {
  "NORTH" => "SOUTH",
  "EAST" => "WEST",
  "SOUTH" => "NORTH",
  "WEST" => "EAST",
}

def dirReduc(arr)
  res = []

  idx = 0

  while idx < arr.size
    if HASH[arr[idx]] == res.last
      res.pop
    else
      res.push(arr[idx])
    end
    idx += 1
  end

  res
end

p dirReduc(["NORTH", "SOUTH", "EAST", "WEST"])
p dirReduc( ["NORTH", "EAST", "WEST", "SOUTH", "WEST", "WEST"])
p dirReduc( ["NORTH", "WEST", "SOUTH", "EAST"])
p dirReduc(["NORTH", "SOUTH", "SOUTH", "EAST", "WEST", "NORTH", "WEST"])
p dirReduc(["NORTH", "SOUTH", "SOUTH", "EAST", "WEST", "NORTH"])