-module(task4).

-export([reverse/1, reverse/3, listLength/1, listLength/2, nth/2, seq/2, seq/5]).

listLength(Xs) -> listLength(Xs, 0).

listLength([], Acc) -> Acc;
    listLength( [_|Xs], Acc) -> listLength(Xs, Acc + 1).

reverse(Xs) -> reverse(Xs, listLength(Xs), []).

reverse(_, 0, Ys) -> Ys;
    reverse([X|Xs], Acc, Ys) -> reverse(Xs , Acc - 1, [X|Ys]).

nth(1, [X|_]) -> X ;
    nth (Acc, [_|Xs]) -> nth (Acc - 1, Xs).

seq (X, Y) -> seq (X, Y, 1, [], 0).

seq (X, Y, Acc, XtoY, _) when length(XtoY) == ((Y-X+Acc) div Acc) -> reverse(XtoY);
    seq (X, Y, Acc, [], I) when ( (Y>(X-Acc)) and (Acc > 0) ) or ( (Y < (X-Acc)) and ((Acc < 0)) ) or ( (Acc == 0) and (X==Y) ) ->
        seq(X, Y, Acc, [X], I+1);
    seq (X, Y, Acc, XtoY, I) when ( (Y>(X-Acc)) and (Acc > 0) ) or ( (Y < (X-Acc)) and ((Acc < 0)) ) or ( (Acc == 0) and (X==Y) ) ->
        seq(X, Y, Acc, [X+Acc*I|XtoY], I+1).