Advent of Code 2021 - Day 21

Questions & Discussions Coding Challenges
1

This topic is about Day 21 of the Advent of Code 2021 .

We have a private leaderboard (shared with users of the elixir forum):

https://adventofcode.com/2021/leaderboard/private/view/370884

The entry code is:
370884-a6a71927

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2

Part1 was simple enough; my solution doesn’t lend itself to part 2

-compile([export_all]).

-record(state, { die_num = 1, 
                 next_pid,
                 pos ,
                 score = 0,
                 die_roll =0
               }).


%% Not reading in input just setting positions. 
-define(P1_START, 1).
-define(P2_START, 10).

p1() ->
    process_flag(trap_exit, true), 
    {ok,P1Pid} = proc_lib:start_link(?MODULE, init, [self(), player1,?P1_START]), 
    {ok, P2Pid }= proc_lib:start_link(?MODULE, init, [self(), player2,?P2_START]), 
    P1Pid ! {set, P2Pid},
    P2Pid ! {set, P1Pid},
    P1Pid ! {run, 1, 0},
    {P1Pid, P2Pid}.



init(PPid, Name, StartPos) ->
    proc_lib:init_ack(PPid, {ok, self()}), 
    register(Name, self()),
    loop(#state{pos = StartPos}).

loop(shutdown) ->
    void;
loop(State) ->
    NewState = receive 
        Msg -> process_msg(Msg, State)
    end,
    loop(NewState).


process_msg({set, Pid} , State) ->
    State#state{next_pid = Pid};
process_msg({run, Die, Rolls}, State= #state{next_pid = NPid}) ->
    Roll = Die * 3 + 3, 
    NewDieCount = Die + 3,
    NewRolls = Rolls + 3,
    case score(Roll, State) of 
        {N, _} when N >= 1000 ->
           %% Win
            NPid ! {lose, NewRolls},
            shutdown;
        {N,NewPos} ->
            NPid ! {run,  NewDieCount, NewRolls},
            State#state{score = N,
                        pos = NewPos
                       }
    end;
process_msg({lose, NewDieCount}, _State = #state{score = Score}) ->
    Output = NewDieCount * Score,
    
    io:format("Answer:~p~n", [Output]), 
    shutdown.


score(Roll, #state{ pos = Pos, 
                    score = Score }) ->
    CurPos = Pos+Roll, 
    NPos = make_1_to_10(CurPos),
    {NPos + Score, NPos}.


%% Sure there is better way. 
make_1_to_10(N) when N >=1, 
                     N =< 10 ->
    N;
make_1_to_10(N) -> make_1_to_10(N-10).
4 Likes