Walk on matrix

implementation

defmodule WalkOnMatrix do
  def start([rows]) when length(rows) < 2, do: rows

  def start([first_row | remaining_rows]) do
    first_row = reverse_row(first_row, [])

    remaining_rows
    |> sort([], first_row)
    |> reverse_row([])
  end

  defp sort([], [], sorted_row), do: sorted_row

  defp sort([head | tail], unsorted_rows, sorted_row) when tail === [] do
    [last_elem | rest] = segregate_last_elem(head, [])
    sorted_row = [last_elem | sorted_row]
    sorted_row = add_to_sorted(rest, sorted_row)

    sort(unsorted_rows, [], sorted_row)
  end

  defp sort([head | tail], unsorted_rows, sorted_row) do
    [last_elem | rest] = segregate_last_elem(head, [])
    sorted_row = [last_elem | sorted_row]
    unsorted_rows = [rest | unsorted_rows]

    sort(tail, unsorted_rows, sorted_row)
  end

  defp add_to_sorted([], sorted), do: sorted

  defp add_to_sorted([head | tail], sorted) do
    add_to_sorted(tail, [head | sorted])
  end

  defp reverse_row([], reversed_row), do: reversed_row

  defp reverse_row([head | tail], reversed_row) do
    reverse_row(tail, [head | reversed_row])
  end

  defp segregate_last_elem([head | tail], unsorted_row)
       when tail === [],
       do: [head | unsorted_row]

  defp segregate_last_elem([head | tail], unsorted_row) do
    segregate_last_elem(tail, [head | unsorted_row])
  end
end

input = [
  [11, 12, 13, 14, 15],
  [24, 25, 26, 27, 16],
  [23, 30, 29, 28, 17],
  [22, 21, 20, 19, 18]
]

two_elem = [
  [1, 2, 3, 4, 5],
  [10, 9, 8, 7, 6]
]

one_elem = [
  [1, 2, 3, 4, 5]
]

WalkOnMatrix.start(one_elem)