day 7 prolog

pl/07.1.pl

@@ -0,0 +1,28 @@
+numbers_strings([], []).
+numbers_strings([A|As], [B|Bs]) :-
+    number_string(A, B),
+    numbers_strings(As, Bs).
+
+read_file(Stream, X) :-
+    \+ at_end_of_stream(Stream),
+    read_line_to_codes(Stream, C),
+    string_chars(S, C),
+    split_string(S, ",", "", Y),
+    numbers_strings(X, Y),
+    at_end_of_stream(Stream).
+
+main :-
+    open('../input/07', read, Stream),
+    read_file(Stream, Lines), !,
+    close(Stream),
+    msort(Lines, L),
+    length(L, Len),
+    I is Len // 2,
+    nth0(I, L, X),
+    calculate_diff(L, X, N),
+    print([X, N]).
+
+calculate_diff([], _, 0).
+calculate_diff([A|As], X, B) :-
+    calculate_diff(As, X, B0),
+    B is B0 + abs(A - X).

pl/07.2.pl

@@ -0,0 +1,41 @@
+numbers_strings([], []).
+numbers_strings([A|As], [B|Bs]) :-
+    number_string(A, B),
+    numbers_strings(As, Bs).
+
+read_file(Stream, X) :-
+    \+ at_end_of_stream(Stream),
+    read_line_to_codes(Stream, C),
+    string_chars(S, C),
+    split_string(S, ",", "", Y),
+    numbers_strings(X, Y),
+    at_end_of_stream(Stream).
+
+main :-
+    open('../input/07', read, Stream),
+    read_file(Stream, Lines), !,
+    close(Stream),
+    msort(Lines, L),
+    min_list(L, A),
+    max_list(L, B),
+    bin_search(A, B, L, N),
+    print(N).
+
+tri(A, B) :-
+    B is (A * (A + 1)) // 2.
+
+calculate_diff([], _, 0).
+calculate_diff([A|As], X, B) :-
+    calculate_diff(As, X, B0),
+    tri(abs(A - X), T),
+    B is B0 + T.
+
+bin_search(L, L, A, Ans) :-
+    calculate_diff(A, L, Ans). 
+bin_search(L, R, A, Ans) :-
+    L < R,
+    M is (L + R) // 2,
+    ((M >= R, A1 is 9999999999999999); bin_search(L, M, A, A1)),
+    ((M =< L, A2 is 9999999999999999); bin_search(M, R, A, A2)),
+    Ans is min(A1, A2).
+