-module(shunt).
-import(list,[position/2,take/2,drop/2,append/2]).
-export([find/2]).
-export([split/2]).
-export([few/2]).

find([],[]) -> [];
find(Xs,Ys)-> {Hs,Ts}=split(Xs,hd(Ys)),
          State = append(Ts,Hs),
              Lone = length(Ts)+1,
              Ltwo = length(Hs),
          [{one,Lone},{two,Ltwo},{one,-Lone},{two,-Ltwo}|find(State,tl(Ys))].

split(Train,E) ->
    N = position(Train,E), {take(Train,N-1),drop(Train,N)}.

few([],[]) -> [];
few(Xs,Ys)->
    if
    hd(Xs) == hd(Ys) ->
        find(tl(Xs),tl(Ys));
        hd(Xs) /= hd(Ys) ->
        {Hs,Ts}=split(Xs,hd(Ys)),
        State = append(Ts,Hs),
        [{one,length(Ts)+1},{two,length(Hs)},{one,-(length(Ts)+1)},{two,-length(Hs)}|find(State,tl(Ys))]
    end.