day 22 solution

day22/Makefile

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+all: day22.beam
+	erl -noshell -s day22 start -s init stop
+
+day22.beam:
+	erlc day22.erl
+
+clean:
+	rm -f day22.beam

day22/day22.erl

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+-module(day22).
+-export([start/0]).
+
+process_input(Filename)
+  -> { ok, Input } = file:read_file(Filename),
+     Lines = re:split(unicode:characters_to_list(string:chomp(Input)), "\n"),
+     { process_line(Lines, 0, maps:new()), (length(Lines) div 2) }.
+
+process_line([], _Index, Map)
+  -> Map;
+process_line([Head|Tail], Index, Map)
+  -> process_line(Tail, Index + 1, process_chars(re:split(Head, ""), Index, 0, Map)).
+
+process_chars([], _Row, _Column, Map)
+  -> Map;
+process_chars([Head|Tail], Row, Column, Map)
+  when Head == <<"#">> -> process_chars(Tail, Row, Column + 1, maps:put({ Column, Row }, infected, Map));
+process_chars([_Head|Tail], Row, Column, Map)
+  -> process_chars(Tail, Row, Column + 1, Map).
+
+run_map(Map, Center)
+  -> run_map(Map, 10000, 0, up, Center, Center, maps:get({ Center, Center }, Map, clean)).
+
+run_map(_Map, Iterations, Infections, _Direction, _X, _Y, _NodeState)
+  when Iterations == 0 -> Infections;
+run_map(Map, Iterations, Infections, Direction, X, Y, NodeState)
+  when NodeState == clean -> NewDirection = turn_left(Direction),
+                             { NewX, NewY } = move(NewDirection, X, Y),
+                             run_map(maps:put({ X, Y }, infected, Map), Iterations - 1, Infections + 1, NewDirection, NewX, NewY, maps:get({ NewX, NewY }, Map, clean));
+run_map(Map, Iterations, Infections, Direction, X, Y, NodeState)
+  when NodeState == infected -> NewDirection = turn_right(Direction),
+                                { NewX, NewY } = move(NewDirection, X, Y),
+                                run_map(maps:put({ X, Y }, clean, Map), Iterations - 1, Infections, NewDirection, NewX, NewY, maps:get({ NewX, NewY }, Map, clean)).
+
+turn_left(Direction)
+  when Direction == up -> left;
+turn_left(Direction)
+  when Direction == left -> down;
+turn_left(Direction)
+  when Direction == down -> right;
+turn_left(Direction)
+  when Direction == right -> up.
+
+turn_right(Direction)
+  when Direction == up -> right;
+turn_right(Direction)
+  when Direction == right -> down;
+turn_right(Direction)
+  when Direction == down -> left;
+turn_right(Direction)
+  when Direction == left -> up.
+
+move(Direction, X, Y)
+  when Direction == up -> { X, Y - 1 };
+move(Direction, X, Y)
+  when Direction == left -> { X - 1, Y };
+move(Direction, X, Y)
+  when Direction == down -> { X, Y + 1 };
+move(Direction, X, Y)
+  when Direction == right -> { X + 1, Y }.
+
+run_map2(Map, Center)
+  -> run_map2(Map, 10000000, 0, up, Center, Center, maps:get({ Center, Center }, Map, clean)).
+
+run_map2(_Map, Iterations, Infections, _Direction, _X, _Y, _NodeState)
+  when Iterations == 0 -> Infections;
+run_map2(Map, Iterations, Infections, Direction, X, Y, NodeState)
+  when NodeState == clean -> NewDirection = turn_left(Direction),
+                             { NewX, NewY } = move(NewDirection, X, Y),
+                             run_map2(maps:put({ X, Y }, weakened, Map), Iterations - 1, Infections, NewDirection, NewX, NewY, maps:get({ NewX, NewY }, Map, clean));
+run_map2(Map, Iterations, Infections, Direction, X, Y, NodeState)
+  when NodeState == weakened -> { NewX, NewY } = move(Direction, X, Y),
+                             run_map2(maps:put({ X, Y }, infected, Map), Iterations - 1, Infections + 1, Direction, NewX, NewY, maps:get({ NewX, NewY }, Map, clean));
+run_map2(Map, Iterations, Infections, Direction, X, Y, NodeState)
+  when NodeState == infected -> NewDirection = turn_right(Direction),
+                                { NewX, NewY } = move(NewDirection, X, Y),
+                                run_map2(maps:put({ X, Y }, flagged, Map), Iterations - 1, Infections, NewDirection, NewX, NewY, maps:get({ NewX, NewY }, Map, clean));
+run_map2(Map, Iterations, Infections, Direction, X, Y, NodeState)
+  when NodeState == flagged -> NewDirection = reverse_direction(Direction),
+                               { NewX, NewY } = move(NewDirection, X, Y),
+                               run_map2(maps:put({ X, Y }, clean, Map), Iterations - 1, Infections, NewDirection, NewX, NewY, maps:get({ NewX, NewY }, Map, clean)).
+
+reverse_direction(Direction)
+  when Direction == up -> down;
+reverse_direction(Direction)
+  when Direction == down -> up;
+reverse_direction(Direction)
+  when Direction == left -> right;
+reverse_direction(Direction)
+  when Direction == right -> left.
+
+start()
+  -> { SampleInput, SampleCenter } = process_input("sample"),
+     io:fwrite("sample center ~p number of infections ~p~n", [SampleCenter, run_map(SampleInput, SampleCenter)]),
+     { ProblemInput, ProblemCenter } = process_input("problem"),
+     io:fwrite("problem center ~p number of infections ~p~n", [ProblemCenter, run_map(ProblemInput, ProblemCenter)]),
+     io:fwrite("sample part 2 center ~p number of infections ~p~n", [SampleCenter, run_map2(SampleInput, SampleCenter)]),
+     io:fwrite("problem part 2 center ~p number of infections ~p~n", [ProblemCenter, run_map2(ProblemInput, ProblemCenter)]).

day22/problem

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+#.###...#..#..#...##.####
+##.##.#..##.#..#.#..#####
+.####..###.#.#####.#.##.#
+##..#.##.#.#.#...#..##..#
+..#...####.#.###.###...#.
+#..###.##.###.....#....#.
+.#..#.##.##....##...####.
+###.##....#...#.##....##.
+..#.###..######.#.####...
+.#.###..#.##.#..##.######
+###.####.#####.####....#.
+#...####.#.##...##..#.#..
+##.######.#....##.#.####.
+.#.#..#...##....#....#...
+.####.##.#..##...#..####.
+.#.####.##..###..###..##.
+...#...####...#.#.#.###.#
+#.##.####.#..##.###.####.
+.#.#...####....##..####.#
+##.###.##..####..#.######
+#.#...#.#.##.####........
+.......#..##..#.#..###...
+.#..###.###........##.#..
+.######.......#.#.##.#.#.
+.##..#.###.....##.#.#...#

day22/sample

@@ -0,0 +1,3 @@
+..#
+#..
+...