/* 

  Advent of Code 2023 Day 16 in Picat.

  https://adventofcode.com/2023/day/16

  This program was created by Hakan Kjellerstrand, hakank@gmail.com
  See also my Picat page: http://www.hakank.org/picat/

*/

import util.

main => go.

go =>
  part1,
  part2,
  nl.

/*
  Part 1:

  $ hyperfine 'picat -g part1 16.pi'
  Benchmark 1: picat -g part1 16.pi
    Time (mean ± σ):      53.4 ms ±   6.4 ms    [User: 34.8 ms, System: 18.5 ms]
    Range (min … max):    37.1 ms …  77.8 ms    45 runs

*/
part1 =>
  M = read_file_lines("16.txt"),
  NumVisits=num_visits(M,M.len,M[1].len,[1,1,west]),
  println(NumVisits).


/*
  Part 2: 

  $ hyperfine 'picat -g part2 16.pi'

  With Ps2 := Ps2 ++ [ [NewI,NewJ,NewFrom] ]:
  Benchmark 1: picat -g part2 16.pi
    Time (mean ± σ):      3.515 s ±  0.029 s    [User: 3.491 s, System: 0.021 s]
    Range (min … max):    3.475 s …  3.577 s    10 runs

  Faster with Ps2 := [[NewI,NewJ,NewFrom]|Ps2] (and a few other tweakings):
    Time (mean ± σ):      2.692 s ±  0.019 s    [User: 2.673 s, System: 0.019 s]
    Range (min … max):    2.668 s …  2.740 s    10 runs

*/
part2 =>
  garbage_collect(100_000_000),
  M = read_file_lines("16.txt"),
  Rows = M.len,
  Cols = M[1].len, 
  Pss = [ [[1,   J,   north] : J in 1..Cols] ,    % top row from north
          [[Rows,J,   south] : J in 1..Cols] , % bottom row from south
          [[I,   1,    west] : I in 1..Rows],      % left column from west
          [[I,   Cols, east] : I in 1..Rows]    % right column from east
      ].flatten.chunks_of(3),
  MaxVisits = 0,
  foreach([StartI,StartJ,StartFrom] in Pss)
    Num = num_visits(M,Rows,Cols,[StartI,StartJ,StartFrom]),
    if Num > MaxVisits then
      MaxVisits := Num
    end
  end,
  println(MaxVisits).


table
num_visits(M,Rows,Cols,[StartI,StartJ,StartDir]) = Map.size =>
  Map = new_set(),  % Number of tiles energized
  Seen = new_set(), % visited [I,J,Dir]
  Ps = [[StartI,StartJ,StartDir]],
  while ([[I,J,From]|Ps2] = Ps)
    Map.put([I,J]),
    new_dir(M[I,J],From,[I,J],Ds),
    foreach([II,JJ,NewFrom] in Ds, NewI=II+0, NewJ=JJ+0, not Seen.has_key([NewI,NewJ,NewFrom]))
      if NewI >= 1, NewI <= Rows, NewJ >= 1, NewJ <= Cols then
        Ps2 := [[NewI,NewJ,NewFrom]|Ps2]
      end
    end,
    Seen.put([I,J,From]),
    Ps := Ps2
  end.

%
% Note: These are _from_ directions, not _to_ directions
%
new_dir('.',north,[I,J],[[I+1,J,north]]).
new_dir('.',south,[I,J],[[I-1,J,south]]).
new_dir('.',west,[I,J],[[I,J+1,west]]).
new_dir('.',east,[I,J],[[I,J-1,east]]).

new_dir('/',north,[I,J],[[I,J-1,east]]).
new_dir('/',south,[I,J],[[I,J+1,west]]).
new_dir('/',west,[I,J],[[I-1,J,south]]).
new_dir('/',east,[I,J],[[I+1,J,north]]).

new_dir('\\',north,[I,J],[[I,J+1,west]]).
new_dir('\\',south,[I,J],[[I,J-1,east]]).
new_dir('\\',west,[I,J],[[I+1,J,north]]).
new_dir('\\',east,[I,J],[[I-1,J,south]]).

% splitters
new_dir('|',north,[I,J],[[I+1,J,north]]).
new_dir('|',south,[I,J],[[I-1,J,south]]).
new_dir('|',west,[I,J],[[I+1,J,north],[I-1,J,south]]).
new_dir('|',east,[I,J],[[I+1,J,north],[I-1,J,south]]).

new_dir('-',north,[I,J],[[I,J+1,west],[I,J-1,east]]).
new_dir('-',south,[I,J],[[I,J+1,west],[I,J-1,east]]).
new_dir('-',west,[I,J],[[I,J+1,west]]).
new_dir('-',east,[I,J],[[I,J-1,east]]).