solution to the heathrow route planning problem from learnyousomeerlang.com

heathrow.erl

-module(heathrow).
-compile([debug_info, export_all]).

mainFunc() ->
BottomGraphVal = {{0,[]},{0,[]}},

MoveCosts = [{50, 10, 30}, {5, 90, 20}, {40, 2, 25}, {10, 8,0}],

AccIn = {BottomGraphVal, [], []},

RetVal = lists:foldl(	fun(X,Acc) -> 
				{AMove, BMove, XMove} = X,
				{{{AVal,AMoves}, {BVal,BMoves}}, AMovesList, BMovesList} = Acc,
				Res = calcNewSetAndMoves({{AVal, AMoves}, {BVal, BMoves}}, AMove, BMove, XMove),
				{{NewASetVal, NewAMoves}, {NewBSetVal, NewBMoves}} = Res,
				{{{NewASetVal, NewAMoves}, {NewBSetVal, NewBMoves}}, [lists:reverse(NewAMoves) | AMovesList], [lists:reverse(NewBMoves) | BMovesList]}
			end, AccIn, MoveCosts),

{{{AVal, APath}, {BVal, BPath}}, _, _} = RetVal,
{{AVal, BVal}, lists:reverse(APath), lists:reverse(BPath)}.


calcNewSetAndMoves(CurValsMoves, AFwd, BFwd, XCross) ->

	{{AVal, AMoves}, {BVal, BMoves}} = CurValsMoves,

	ValToAStraightFromA = AVal + AFwd,
	ValToACrossFromB = BVal + BFwd + XCross,

	NewASetVal = erlang:min(ValToAStraightFromA, ValToACrossFromB),

NewAMoves = 
	if ValToAStraightFromA < ValToACrossFromB ->
			[aFwd | AMoves];
		true -> % works as an else branch
			[xCross , bFwd | BMoves]
	end,

%-------------------------

ValToBStraightFromB = BVal + BFwd,
ValToBCrossFromA = AVal + AFwd + XCross,

NewBSetVal = erlang:min(ValToBStraightFromB, ValToBCrossFromA),

NewBMoves = 
	if ValToBStraightFromB < ValToBCrossFromA ->
			[bFwd | BMoves];
		true -> % works as an else branch
			[xCross, aFwd | AMoves]
	end,

{{NewASetVal, NewAMoves}, {NewBSetVal, NewBMoves}}.