commit bb300da9d89fe090b7a7e26d8ac31dca2dbaaee5
from: Lukas Henkel <lh@entf.net>
date: Thu Dec 04 12:42:35 2025 UTC

Day 4

commit - ca2c4eaaf9aba78538be353cbdc628cf21b35424
commit + bb300da9d89fe090b7a7e26d8ac31dca2dbaaee5
blob - /dev/null
blob + eb05bf3856a27a93be766a42bb3f3477acf31c0f (mode 644)
--- /dev/null
+++ 04.pl
@@ -0,0 +1,62 @@
+parse_input(File) :-
+    read_file_to_string(File, Content, []),
+    split_string(Content, "\n", "", Lines0),
+    exclude(=(""), Lines0, Lines),
+    length(Lines, Length),
+    numlist(1, Length, Ys),
+    maplist(assert_line, Lines, Ys).
+
+assert_line(Line, Y) :-
+    string_chars(Line, Chars),
+    assert_chars(Chars, 1, Y).
+
+assert_chars([], _, _).
+assert_chars([C|Rest], X, Y) :-
+    assert_field(C, X, Y),
+    X2 is X + 1,
+    assert_chars(Rest, X2, Y).
+
+assert_field('@', X, Y) :-
+    assertz(roll(X, Y)).
+assert_field(_, _, _).
+
+forklift_access(X, Y) :-
+    roll(X, Y),
+    neighbour_count(X, Y, N),
+    N < 4.
+
+neighbour_offset(DX, DY) :-
+    between(-1, 1, DX),
+    between(-1, 1, DY),
+    \+ (DX = 0, DY = 0).
+
+has_neighbour(X, Y, DX, DY) :-
+    neighbour_offset(DX, DY),
+    NX is X + DX,
+    NY is Y + DY,
+    roll(NX, NY).
+
+neighbour_count(X, Y, N) :-
+    aggregate_all(count, has_neighbour(X, Y, _, _), N).
+
+task1(N) :-
+    aggregate_all(count, forklift_access(_, _), N).
+
+task2_(C0, Total) :-
+    findall(roll(X, Y), forklift_access(X, Y), List),
+    maplist(retract, List),
+    length(List, C1),
+    C3 is C0 + C1,
+    ( C1 = 0
+    -> Total is C3
+    ;  task2_(C3, Total)
+    ).
+
+task2(N) :-
+    task2_(0, N).
+
+:-
+    parse_input("input/04.txt"),
+    task1(Task1),
+    task2(Task2),
+    format("~d ~d~n", [Task1, Task2]).