day23 solution, helped by reddit

day23/Makefile

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+all: day23.beam
+	erl -noshell -s day23 start -s init stop
+
+day23.beam:
+	erlc day23.erl
+
+clean:
+	rm -f day23.beam

day23/day23.erl

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+-module(day23).
+-export([start/0]).
+
+value_or_register(X, Registers)
+  when X >= <<"a">>, X =< <<"z">> -> maps:get(X, Registers, 0);
+value_or_register(X, _Registers)
+  -> { NewValue, _ } = string:to_integer(X),
+     NewValue.
+
+format_input(Input)
+  -> lists:map(fun(X) -> [A|Args] = re:split(X, " "), { A, Args } end, re:split(Input, "\n")).
+
+assemble(Input)
+  -> Instructions = format_input(Input),
+     assemble(Instructions, length(Instructions), 1, 0, maps:new()).
+
+debug_assemble(Input)
+  -> Instructions = format_input(Input),
+     assemble(Instructions, length(Instructions), 1, 0, maps:put(<<"a">>, 1, maps:new())).
+
+assemble(_Instructions, MaxInstructions, Ip, LastFrequency, Registers)
+  when Ip < 1; Ip > MaxInstructions -> { LastFrequency, Registers };
+assemble(Instructions, MaxInstructions, Ip, LastFrequency, Registers)
+  -> { Op, Args } = lists:nth(Ip, Instructions),
+     %io:fwrite("ip ~p op ~p args ~p~n~p~n", [Ip, Op, Args, Registers]),
+     case Op of
+       <<"add">> ->
+         [Src,Dest|_] = Args,
+         ExistingValue = maps:get(Src, Registers, 0),
+         NewValue = value_or_register(Dest, Registers),
+         assemble(Instructions, MaxInstructions, Ip + 1, LastFrequency, maps:put(Src, ExistingValue + NewValue, Registers));
+       <<"sub">> ->
+         [Src,Dest|_] = Args,
+         ExistingValue = maps:get(Src, Registers, 0),
+         NewValue = value_or_register(Dest, Registers),
+         assemble(Instructions, MaxInstructions, Ip + 1, LastFrequency, maps:put(Src, ExistingValue - NewValue, Registers));
+       <<"jnz">> ->
+         [Src,Dest|_] = Args,
+         SrcValue = value_or_register(Src, Registers),
+         NewValue = value_or_register(Dest, Registers),
+         if SrcValue /= 0 -> assemble(Instructions, MaxInstructions, Ip + NewValue, LastFrequency, Registers);
+            true -> assemble(Instructions, MaxInstructions, Ip + 1, LastFrequency, Registers)
+         end;
+       <<"jgz">> ->
+         [Src,Dest|_] = Args,
+         SrcValue = value_or_register(Src, Registers),
+         NewValue = value_or_register(Dest, Registers),
+         if SrcValue > 0 -> assemble(Instructions, MaxInstructions, Ip + NewValue, LastFrequency, Registers);
+            true -> assemble(Instructions, MaxInstructions, Ip + 1, LastFrequency, Registers)
+         end;
+       <<"mod">> ->
+         [Src,Dest|_] = Args,
+         ExistingValue = maps:get(Src, Registers, 0),
+         NewValue = value_or_register(Dest, Registers),
+         assemble(Instructions, MaxInstructions, Ip + 1, LastFrequency, maps:put(Src, ExistingValue rem NewValue, Registers));
+       <<"mul">> ->
+         [Src,Dest|_] = Args,
+         ExistingValue = maps:get(Src, Registers, 0),
+         NewValue = value_or_register(Dest, Registers),
+         Registers2 = maps:put("mul_count", maps:get("mul_count", Registers, 0) + 1, Registers),
+         assemble(Instructions, MaxInstructions, Ip + 1, LastFrequency, maps:put(Src, ExistingValue * NewValue, Registers2));
+       <<"rcv">> ->
+         [Dest|_] = Args,
+         NewValue = value_or_register(Dest, Registers),
+         if NewValue /= 0 -> LastFrequency;
+            true -> assemble(Instructions, MaxInstructions, Ip + 1, LastFrequency, Registers)
+         end;
+       <<"set">> ->
+         [Src,Dest|_] = Args,
+         NewValue = value_or_register(Dest, Registers),
+         assemble(Instructions, MaxInstructions, Ip + 1, LastFrequency, maps:put(Src, NewValue, Registers));
+       <<"snd">> ->
+         [Dest|_] = Args,
+         NewValue = value_or_register(Dest, Registers),
+         assemble(Instructions, MaxInstructions, Ip + 1, NewValue, Registers);
+        <<>> ->
+         io:fwrite("invalid instruction: ~p~n", [{ Op, Args }]),
+         assemble(Instructions, MaxInstructions, Ip + 1, LastFrequency, Registers)
+    end.
+
+is_prime(Check)
+  -> is_prime(Check, 2, math:sqrt(Check)).
+is_prime(Check, Min, _Max)
+  when Check rem Min == 0 -> false;
+is_prime(Check, Min, Max)
+  when Min > Max -> Check /= 1;
+is_prime(Check, Min, Max)
+  -> is_prime(Check, Min + 1, Max).
+
+get_num_nonprimes(Start, End)
+  -> get_num_nonprimes(Start, End, 1, is_prime(Start)).
+get_num_nonprimes(Start, End, Count, _IsPrime)
+  when Start == End -> Count;
+get_num_nonprimes(Start, End, Count, IsPrime)
+  when IsPrime -> NewStart = Start + 17,
+                  get_num_nonprimes(NewStart, End, Count, is_prime(NewStart));
+get_num_nonprimes(Start, End, Count, IsPrime)
+  when not IsPrime -> NewStart = Start + 17,
+                      get_num_nonprimes(NewStart, End, Count + 1, is_prime(NewStart)).
+
+start()
+  -> { ok, File } = file:read_file("problem"),
+     io:fwrite("~p~n", [ assemble(File) ]),
+     %io:fwrite("~p~n", [ debug_assemble(File) ]).
+     io:fwrite("~p~n", [ get_num_nonprimes(109900, 126900) ]).

day23/problem

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+set b 99
+set c b
+jnz a 2
+jnz 1 5
+mul b 100
+sub b -100000
+set c b
+sub c -17000
+set f 1
+set d 2
+set e 2
+set g d
+mul g e
+sub g b
+jnz g 2
+set f 0
+sub e -1
+set g e
+sub g b
+jnz g -8
+sub d -1
+set g d
+sub g b
+jnz g -13
+jnz f 2
+sub h -1
+set g b
+sub g c
+jnz g 2
+jnz 1 3
+sub b -17
+jnz 1 -23