solve 2015 day 14

2015/README.md

@@ -12,12 +12,12 @@
   ```
 </details>
 
-|   S  |  M  |  T  |  W  |  T   |  F   |  S   |
-| :--: | :-: | :-: | :-: | :-:  | :-:  | :-:  |
-|      |     | [1] | [2] | [3]  | [4]  | [5]  |
-|  [6] | [7] | [8] | [9] | [10] | [11] | [12] |
-| [13] | 14  | 15  | 16  | 17   | 18   | 19   |
-|  20  | 21  | 22  | 23  | 24   | 25   |      |
+|  S   |  M   |  T  |  W  |  T   |  F   |  S   |
+| :--: | :--: | :-: | :-: | :-:  | :-:  | :-:  |
+|      |      | [1] | [2] | [3]  | [4]  | [5]  |
+|  [6] | [7]  | [8] | [9] | [10] | [11] | [12] |
+| [13] | [14] | 15  | 16  | 17   | 18   | 19   |
+|  20  | 21   | 22  | 23  | 24   | 25   |      |
 
 [1]: ./lib/2015/1.ex
 [2]: ./lib/2015/2.ex
@@ -32,3 +32,4 @@
 [11]: ./lib/2015/11.ex
 [12]: ./lib/2015/12.ex
 [13]: ./lib/2015/13.ex
+[14]: ./lib/2015/14.ex

2015/lib/2015/14.ex

@@ -0,0 +1,58 @@
+import AOC
+
+aoc 2015, 14 do
+  @end_time 2503
+
+  def parse_line(line) do
+    Regex.run(
+      ~r/^\w+ can fly (\d+) km\/s for (\d+) seconds, but then must rest for (\d+) seconds.$/,
+      line,
+      capture: :all_but_first
+    )
+    |> Enum.map(&String.to_integer/1)
+  end
+
+  def distance_traveled(speed, run, rest, time) do
+    full_cycle = run + rest
+    full_cycles = div(time, full_cycle)
+
+    time_into_current_cycle = rem(time, run + rest)
+
+    total_running_time = full_cycles * run + min(time_into_current_cycle, run)
+
+    total_running_time * speed
+  end
+
+  def p1 do
+    input_stream()
+    |> Stream.map(&parse_line/1)
+    |> Stream.map(fn [speed, run, rest] -> distance_traveled(speed, run, rest, @end_time) end)
+    |> Enum.max()
+  end
+
+  def p2 do
+    reindeer =
+      input_stream()
+      |> Enum.map(&parse_line/1)
+      |> Enum.map(&{0, &1})
+
+    for s <- 1..@end_time, reduce: reindeer do
+      reindeer ->
+        winning_distance =
+          reindeer
+          |> Enum.map(fn {_, [speed, run, rest]} -> distance_traveled(speed, run, rest, s) end)
+          |> Enum.max()
+
+        reindeer
+        |> Enum.map(fn {score, [speed, run, rest] = properties} ->
+          if distance_traveled(speed, run, rest, s) == winning_distance do
+            {score + 1, properties}
+          else
+            {score, properties}
+          end
+        end)
+    end
+    |> Enum.map(&elem(&1, 0))
+    |> Enum.max()
+  end
+end