4 files changed, 119 insertions, 11 deletions
diff --git a/challenge-281/packy-anderson/elixir/ch-2.exs b/challenge-281/packy-anderson/elixir/ch-2.exs
index 04b5c8529b..1009526549 100755
--- a/challenge-281/packy-anderson/elixir/ch-2.exs
+++ b/challenge-281/packy-anderson/elixir/ch-2.exs
@@ -1,20 +1,128 @@
 #!/usr/bin/env elixir
 
 defmodule PWC do
+  defp letterAdd(letter, add) do
+    <<val::utf8>> = letter
+    List.to_string([val + add])
+  end
+
+  def onBoard(c,r) do
+    "a" <= c and c <= "h" and 1 <= r and r <= 8
+  end
+
+  defp knightMoveList(), do: [
+    {-2, -1}, {-2, +1}, {-1, -2}, {-1, +2},
+    {+2, -1}, {+2, +1}, {+1, -2}, {+1, +2},
+  ]
+
+  def knightMoves([], _, _, endpoints), do: endpoints
+
+  def knightMoves([next | rest], letter, num, endpoints) do
+    {col, row} = next
+    newcol = letterAdd(letter, col)
+    newrow = num + row
+    endpoints = if onBoard(newcol,newrow) do
+      # add to list being returned
+      endpoints ++ [ newcol <> to_string(newrow) ]
+    else
+      endpoints
+    end
+    knightMoves(rest, letter, num, endpoints)
+  end
+
+  def knightMoves(coordinates) do
+    letter = String.first(coordinates)
+    {num, _} = Integer.parse(String.last(coordinates))
+    knightMoves(knightMoveList(), letter, num, [])
+  end
+
+  def processEndpoints(
+    next, params = %{
+      moves_to: moves_to,
+      path_to:  path_to,
+      startPos: startPos,
+      endPos:   endPos,
+      queue:    queue
+    }
+  ) do
+    # update the move count map
+    moves_to = Map.put(moves_to, next, moves_to[startPos] + 1)
+
+    # update the path to current space map
+    path_to = Map.put(path_to, next,
+      "#{path_to[startPos]} -> #{next}"
+    )
+
+    if next == endPos do
+      # we found the shortest path, update the return
+      # values which will stop the loop
+      %{ moves: moves_to[next], path: path_to[next] }
+    else
+      # update params for next iteration
+      params |> Map.put(:moves_to, moves_to)
+             |> Map.put(:path_to,  path_to)
+             |> Map.put(:queue,    queue ++ [ next ])
+    end
+  end
+
+  def processEndpoints(_, params = %{moves: moves})
+    when not is_nil(moves), do: params
+
+  # we've exhausted the queue
+  # (only possible when the chessboard is an odd size)
+  def processQueue([], _), do: %{
+    moves: -1, path: "no path found"
+  }
+
+  def processQueue(_, params = %{moves: moves})
+    when not is_nil(moves), do: params
+
+  def processQueue([startPos | queue], params = %{
+    path_to: path_to
+  }) do
+    # put the current starting position and the current queue
+    # into the params
+    params = params |> Map.put(:queue,    queue)
+                    |> Map.put(:startPos, startPos)
+
+    # figure out the valid moves that we haven't been to yet
+    endpoints = knightMoves(startPos)
+    |> Enum.filter(fn m -> !Map.has_key?(path_to, m) end)
+
+    # call processEndpoints/2 for each of the endpoints
+    params = Enum.reduce(endpoints, params, &processEndpoints/2)
+
+    # recursively call to process the rest of the queue
+    processQueue(params[:queue], params)
+  end
+
+  # trivial case: we're already at the end point
+  def leastMoves(startPos, endPos) when startPos == endPos, do:
+    { 0, endPos }
+
+  def leastMoves(startPos, endPos) do
+    params = processQueue([ startPos ], %{
+      endPos:   endPos,
+      moves_to: %{ startPos => 0 },
+      path_to:  %{ startPos => startPos },
+      moves:    nil,
+      path:     nil
+    })
+    { params[:moves], params[:path] }
+  end
 
-  def solution(ints) do
-    IO.puts("Input: @ints = (" <> Enum.join(ints, ", ") <> ")")
-    {sign, explain} = PWC.productSign(ints)
-    IO.puts("Output: " <> to_string(sign) )
-    IO.puts("\n" <> explain)
+  def solution(startPos, endPos) do
+    IO.puts("Input: $start = '#{startPos}', $end = '#{endPos}'")
+    {count, moves} = leastMoves(startPos, endPos)
+    IO.puts("Output: #{to_string(count)}\n\n#{moves}" )
   end
 end
 
 IO.puts("Example 1:")
-PWC.solution()
+PWC.solution("g2", "a8")
 
 IO.puts("\nExample 2:")
-PWC.solution()
+PWC.solution("g2", "h2")
 
 IO.puts("\nExample 3:")
-PWC.solution()
+PWC.solution("a1", "h8")
diff --git a/challenge-281/packy-anderson/perl/ch-2.pl b/challenge-281/packy-anderson/perl/ch-2.pl
index 92eeb1cbd4..3992136a60 100755
--- a/challenge-281/packy-anderson/perl/ch-2.pl
+++ b/challenge-281/packy-anderson/perl/ch-2.pl
@@ -68,7 +68,7 @@ sub solution($start, $end) {
   say qq/Input: \$start = '$start', \$end = '$end'/;
   my ($count, $moves) = leastMoves($start, $end);
   say 'Output: ' . $count;
-  say "\n$moves\n";
+  say "\n$moves";
 }
 
 say "Example 1:";
diff --git a/challenge-281/packy-anderson/python/ch-2.py b/challenge-281/packy-anderson/python/ch-2.py
index f1b8803a71..72f51c823f 100755
--- a/challenge-281/packy-anderson/python/ch-2.py
+++ b/challenge-281/packy-anderson/python/ch-2.py
@@ -65,7 +65,7 @@ def leastMoves(start, end):
 def solution(start, end):
     print(f'Input: $start = \'{start}\', $end = \'{end}\'')
     count, moves = leastMoves(start, end)
-    print(f'Output: {count}\n\n{moves}\n')
+    print(f'Output: {count}\n\n{moves}')
 
 print('Example 1:')
 solution('g2', 'a8')
diff --git a/challenge-281/packy-anderson/raku/ch-2.raku b/challenge-281/packy-anderson/raku/ch-2.raku
index 4ab5b7f4b1..ed29559b0a 100755
--- a/challenge-281/packy-anderson/raku/ch-2.raku
+++ b/challenge-281/packy-anderson/raku/ch-2.raku
@@ -68,7 +68,7 @@ sub solution($start, $end) {
   say qq/Input: \$start = '$start', \$end = '$end'/;
   my ($count, $moves) = leastMoves($start, $end);
   say 'Output: ' ~ $count;
-  say "\n$moves\n";
+  say "\n$moves";
 }
 
 say "Example 1:";