%%% list comprehension examples
%%% http://www.erlang.org/doc/programming_examples/list_comprehensions.html

-module(lc).
-compile(export_all).

sort([Pivot|T]) ->
    sort([ X || X <- T, X < Pivot]) ++
    [Pivot] ++
    sort([ X || X <- T, X >= Pivot]);
sort([]) -> [].


perms([]) -> [[]];
perms(L)  -> [[H|T] || H <- L, T <- perms(L--[H])].


sorted([]) -> true;
sorted([X|L]) -> sorted(L,X).

sorted([Head|_Tail], X) when X > Head -> false;
sorted(L,_) -> sorted(L).


permSort(L) -> Perms = perms(L), [X] = lists:filter( fun(L1) -> sorted(L1) end, Perms), X.

	    
		
pyth(N) ->
    [ {A,B,C} ||
        A <- lists:seq(1,N),
        B <- lists:seq(1,N),
        C <- lists:seq(1,N),
        A+B+C =< N,
        A*A+B*B == C*C 
    ].


pyth1(N) ->
    [ {A,B,C} ||
        A <- safe_seq(1,N-2),
        B <- safe_seq(A+1,N-A-1),
        C <- safe_seq(B+1,N-A-B),
        A+B+C =< N,
        A*A+B*B == C*C 
    ].


safe_seq(Min,Max) when Min > Max -> [];
safe_seq(Min,Max) -> lists:seq(Min,Max).


map( F, L) -> [ F(X) || X <- L ].
filter(Pred, L) -> [X || X <- L, Pred(X)].
append(L)   ->  [X || L1 <- L, X <- L1].