commit

day17/day17.erl

@@ -0,0 +1,68 @@
+%% to compile: erlc day3A.erl
+%% to run: erl -noshell -s day5 solve
+%%
+-module(day17).
+
+-export ([solve/0, solve/1, solve/2]).
+-compile ([export_all]).
+
+solve() ->
+    solve(['1']),
+    solve(['2']),
+    init:stop().
+
+solve(A) ->
+    solve(A, read_input()).
+
+solve(['1'], D) ->
+    io:format("The solution to ~p puzzle1 is: ~p~n", [?MODULE, solve(1, D)]);
+solve(1, D) ->
+    solution1(D);
+solve(['2'], D) ->
+    io:format("The solution to ~p puzzle2 is: ~p~n", [?MODULE, solve(2, D)]);
+solve(2, D) ->
+    solution2(D).
+
+solution1({X,Y}) ->
+    Xs = find_x(X),
+    Ys = find_y(Y),
+    {T, X1, Y1} = lists:max([{Key, X1, proplists:get_value(Key,Ys)} || {Key, X1} <- Xs, lists:keysearch(Key, 1, Ys) /= false]),
+    y_max(T,Y1,0).
+    
+solution2({X,Y}) ->
+    Xs = find_x(X),
+    Ys = find_y(Y),
+    length(lists:usort([{X,Y} || {Ty, Y} <- Ys, {T,X} <- lists:filter(fun({T,X}) -> T == Ty end, Xs)])).
+
+read_input() ->
+    {{124,174},{-123, -86}}.
+%%    {{20,30},{-10, -5}}.
+
+find_x({Xmin, Xmax}) ->
+    [ {T, Xstart}  || Xstart <- lists:seq(0,400), T <- lists:seq(1,1000),  x(Xstart, T) >= Xmin, x(Xstart, T) =< Xmax ].
+
+find_y({Ymin, Ymax}) ->
+    [ {T, Ystart}  || Ystart <- lists:seq(-400,400), T <- lists:seq(1,1000), y(Ystart, T) >= Ymin, y(Ystart, T) =< Ymax ].
+
+x(Xstart, T) ->
+    Last = 
+    case (Xstart - T + 1) of
+        L when L < 0 -> 0;
+        L -> L
+    end,
+    (Xstart - Last + 1) * (Xstart + Last) div 2.
+   
+y(Ystart, T) ->
+    Last = (Ystart - T + 1),
+    (Ystart - Last + 1) * (Ystart + Last) div 2.
+
+y_max(0, _, Ymax) -> Ymax;
+y_max(T, Y, Ymax)  ->
+    NewY = y(Y, T),
+    NewMax = 
+    case  NewY of
+        M when M > Ymax -> M;
+        _ -> Ymax
+    end,
+    y_max(T-1, Y, NewMax).
+