Add 2024/day1/part2.erl

2024/day1/part2.erl

@@ -0,0 +1,30 @@
+-module(day1_part2).
+-export([main/0]).
+
+% Main entry point
+main() ->
+    {ok, Content} = file:read_file("input.txt"),
+    Lines = string:split(string:trim(Content), "\n", all),
+    {List1, List2} = lists:foldl(fun parse_line/2, {[], []}, Lines),
+    CountMap = build_count_map(List2),
+    SimilarityScore = calculate_similarity_score(List1, CountMap),
+    io:format("Result: ~p~n", [SimilarityScore]).
+
+% Parse a single line into two integers and accumulate them into lists
+parse_line(Line, {Acc1, Acc2}) ->
+    [Str1, Str2] = string:split(string:trim(Line), "   ", all),
+    {Num1, _} = string:to_integer(Str1),
+    {Num2, _} = string:to_integer(Str2),
+    {[Num1 | Acc1], [Num2 | Acc2]}.
+
+% Build a map of counts for elements in List2
+build_count_map(List) ->
+    lists:foldl(fun(Elem, Acc) ->
+        maps:update_with(Elem, fun(Count) -> Count + 1 end, 1, Acc)
+    end, #{}, List).
+
+% Calculate the total similarity score
+calculate_similarity_score(List1, CountMap) ->
+    lists:foldl(fun(Elem, Acc) ->
+        Acc + Elem * maps:get(Elem, CountMap, 0)
+    end, 0, List1).