2016 Update

Task/Cut-a-rectangle/Elixir/cut-a-rectangle-1.elixir

@@ -0,0 +1,41 @@
+import  Integer
+
+defmodule Rectangle do
+  def cut_it(h, w) when is_odd(h) and is_odd(w), do: 0
+  def cut_it(h, w) when is_odd(h), do: cut_it(w, h)
+  def cut_it(_, 1), do: 1
+  def cut_it(h, 2), do: h
+  def cut_it(2, w), do: w
+  def cut_it(h, w) do
+    grid = List.duplicate(false, (h + 1) * (w + 1))
+    t = div(h, 2) * (w + 1) + div(w, 2)
+    if is_odd(w) do
+      grid = grid |> List.replace_at(t, true) |> List.replace_at(t+1, true)
+      walk(h, w, div(h, 2), div(w, 2) - 1, grid) + walk(h, w, div(h, 2) - 1, div(w, 2), grid) * 2
+    else
+      grid = grid |> List.replace_at(t, true)
+      count = walk(h, w, div(h, 2), div(w, 2) - 1, grid)
+      if h == w, do: count * 2,
+               else: count + walk(h, w, div(h, 2) - 1, div(w, 2), grid)
+    end
+  end
+
+  defp walk(h, w, y, x, grid, count\\0)
+  defp walk(h, w, y, x,_grid, count) when y in [0,h] or x in [0,w], do: count+1
+  defp walk(h, w, y, x, grid, count) do
+    blen = (h + 1) * (w + 1) - 1
+    t = y * (w + 1) + x
+    grid = grid |> List.replace_at(t, true) |> List.replace_at(blen-t, true)
+    Enum.reduce(next(w), count, fn {nt, dy, dx}, cnt ->
+      if Enum.at(grid, t+nt), do: cnt, else: cnt + walk(h, w, y+dy, x+dx, grid)
+    end)
+  end
+
+  defp next(w), do: [{w+1, 1, 0}, {-w-1, -1, 0}, {-1, 0, -1}, {1, 0, 1}]  # {next,dy,dx}
+end
+
+Enum.each(1..9, fn w ->
+  Enum.each(1..w, fn h ->
+    if is_even(w * h), do: IO.puts "#{w} x #{h}: #{Rectangle.cut_it(w, h)}"
+  end)
+end)