re-organise repo

2023-11-16 10:48:53 +00:00
parent f62c52d8a9
commit f133e157a1
87 changed files with 11792 additions and 0 deletions
--- a/2021/day9/day9.erl
+++ b/2021/day9/day9.erl
@@ -0,0 +1,93 @@
+%% to compile: erlc day3A.erl
+%% to run: erl -noshell -s day3 solve
+%%
+-module(day9).
+
+-export ([solve/0, solve/1, solve/2]).
+-export ([read_input/0]).
+
+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).
+
+read_input() ->
+	{ok, IO} = file:open("input.txt", 'read'),
+	Data = read_input(IO),
+	file:close(IO),
+        Data.
+
+read_input(IO) ->
+	read_input(IO, []).
+
+read_input(IO, Input) ->
+	case read_line(IO) of
+		'eof' -> Input;
+		Line -> read_input(IO, Input ++ [Line])
+	end.
+
+read_line(IO) ->
+	case file:read_line(IO) of
+		'eof' -> 'eof';
+		{ok, Line} -> [ X - $0 || X <- Line, [X] /= "\n"]
+	end.
+
+solution1(Table) ->
+  Low_points = low_points(Table),
+  lists:foldl(fun(C, Acc) -> Acc + 1 + get_value(C, Table) end, 0, Low_points).
+
+solution2(Table) ->
+  Low_points = low_points(Table),
+  Basins = get_basins(Low_points, Table),
+  [B1,B2,B3|_] = lists:sort(fun(A, B) -> length(A) > length(B) end, Basins),
+  length(B1) * length(B2) * length(B3).
+
+
+get_basins(Low_points, Table) ->
+	get_basins(Low_points, Table, []).
+
+get_basins([], _Table, Basins) -> Basins;
+get_basins([Low_point|Rest], Table, Basins) ->
+  Basin = [Low_point|get_up_slopes([Low_point], Table)],
+  get_basins(Rest, Table, [Basin|Basins]).
+
+low_points([H|_] =  Table) ->
+  X = length(H),
+  Y = length(Table),
+  Coords = lists:flatten([[{A,B} || A <- lists:seq(1,X)] || B <- lists:seq(1,Y)]),
+  lists:filter(fun(C) -> is_low_point(C, Table) end, Coords).
+
+get_up_slopes(Coords, Table) ->
+	get_up_slopes(Coords, Table, []).
+
+get_up_slopes([], _Table, Acc) -> Acc;
+get_up_slopes([{X, Y}|Rest], Table, Acc) ->
+    V = get_value({X,Y}, Table),
+    Neighbours = [{X+1, Y},{X-1, Y},{X, Y+1},{X, Y-1}],
+    Up_slopes = lists:filter(fun({X1,Y1}) -> C = get_value({X1,Y1}, Table), C /= 9 andalso C > V end, Neighbours),
+    get_up_slopes(lists:usort(Rest ++ Up_slopes), Table, lists:usort(Acc ++ Up_slopes)).
+
+is_low_point({X,Y}, Table) ->
+    V = get_value({X,Y}, Table),
+    V < get_value({X+1, Y}, Table) andalso
+    V < get_value({X-1, Y}, Table) andalso
+    V < get_value({X, Y+1}, Table) andalso
+    V < get_value({X, Y-1}, Table).
+
+get_value({X,Y}, [H|_] = Table) when X == 0; Y == 0; Y > length(Table); X > length(H) -> 9;
+
+get_value({X,Y}, Table) ->
+	lists:nth(X, lists:nth(Y, Table)).
+