From 28e733e405fcd57fa123ad2f62814da1f5f3700f Mon Sep 17 00:00:00 2001
From: Martin Frost <martin@frost.codes>
Date: Thu, 19 Dec 2024 10:44:27 +0100
Subject: [PATCH] Solve day 3

---
 priv/test_input/3_2.txt |  1 +
 src/day_3.erl           | 34 +++++++++++++++++++++++++++-------
 2 files changed, 28 insertions(+), 7 deletions(-)
 create mode 100644 priv/test_input/3_2.txt

diff --git a/priv/test_input/3_2.txt b/priv/test_input/3_2.txt
new file mode 100644
index 0000000..30032cb
--- /dev/null
+++ b/priv/test_input/3_2.txt
@@ -0,0 +1 @@
+xmul(2,4)&mul[3,7]!^don't()_mul(5,5)+mul(32,64](mul(11,8)undo()?mul(8,5))
diff --git a/src/day_3.erl b/src/day_3.erl
index cdad017..66e9739 100644
--- a/src/day_3.erl
+++ b/src/day_3.erl
@@ -20,7 +20,9 @@ part_2() ->
 
 part_2(Filename) ->
     Input = read_input(Filename),
-    0.
+    Pairs = parse_2(Input),
+    Products = lists:map(fun({A, B}) -> A * B end, Pairs),
+    lists:sum(Products).
 
 %% Private Functions
 
@@ -49,6 +51,26 @@ parse(<<"">>, Pairs) ->
 
 make_pair(A, B) -> {binary_to_integer(A), binary_to_integer(B)}.
 
+parse_2(Binary) ->
+    parse_2(enabled, Binary, []).
+
+parse_2(enabled, <<"mul(",A:1/binary,",",B:1/binary,")",Rest/binary>>, Pairs) -> parse_2(enabled, Rest, [make_pair(A, B) | Pairs]);
+parse_2(enabled, <<"mul(",A:1/binary,",",B:2/binary,")",Rest/binary>>, Pairs) -> parse_2(enabled, Rest, [make_pair(A, B) | Pairs]);
+parse_2(enabled, <<"mul(",A:1/binary,",",B:3/binary,")",Rest/binary>>, Pairs) -> parse_2(enabled, Rest, [make_pair(A, B) | Pairs]);
+parse_2(enabled, <<"mul(",A:2/binary,",",B:1/binary,")",Rest/binary>>, Pairs) -> parse_2(enabled, Rest, [make_pair(A, B) | Pairs]);
+parse_2(enabled, <<"mul(",A:2/binary,",",B:2/binary,")",Rest/binary>>, Pairs) -> parse_2(enabled, Rest, [make_pair(A, B) | Pairs]);
+parse_2(enabled, <<"mul(",A:2/binary,",",B:3/binary,")",Rest/binary>>, Pairs) -> parse_2(enabled, Rest, [make_pair(A, B) | Pairs]);
+parse_2(enabled, <<"mul(",A:3/binary,",",B:1/binary,")",Rest/binary>>, Pairs) -> parse_2(enabled, Rest, [make_pair(A, B) | Pairs]);
+parse_2(enabled, <<"mul(",A:3/binary,",",B:2/binary,")",Rest/binary>>, Pairs) -> parse_2(enabled, Rest, [make_pair(A, B) | Pairs]);
+parse_2(enabled, <<"mul(",A:3/binary,",",B:3/binary,")",Rest/binary>>, Pairs) -> parse_2(enabled, Rest, [make_pair(A, B) | Pairs]);
+parse_2(enabled, <<"don't()",Rest/binary>>, Pairs) -> parse_2(disabled, Rest, Pairs);
+parse_2(disabled, <<"do()",Rest/binary>>, Pairs) -> parse_2(enabled, Rest, Pairs);
+parse_2(State, <<_:8,Rest/binary>>, Pairs) ->
+    parse_2(State, Rest, Pairs);
+parse_2(_State, <<_Whatever:8>>, Pairs) ->
+    Pairs;
+parse_2(_State, <<"">>, Pairs) ->
+    Pairs.
 
 %% TESTS
 
@@ -56,13 +78,11 @@ make_pair(A, B) -> {binary_to_integer(A), binary_to_integer(B)}.
 -include_lib("eunit/include/eunit.hrl").
 
 part_1_test() ->
-    TestFile = test_data(),
+    TestFile = filename:absname("./priv/test_input/3.txt"),
     ?assertEqual(161, part_1(TestFile)).
 
-%% part_2_test() ->
-%%     TestFile = test_data(),
-%%     ?assertEqual(4, part_2(TestFile)).
+part_2_test() ->
+    TestFile = filename:absname("./priv/test_input/3_2.txt"),
+    ?assertEqual(48, part_2(TestFile)).
 
-test_data() ->
-    filename:absname("./priv/test_input/3.txt").
 -endif.