From 0cb6fcf521c2f754aa6cbc2a039c8eaa7e166e63 Mon Sep 17 00:00:00 2001
From: Andrew Coleman <penguincoder@gmail.com>
Date: Sun, 17 Dec 2017 23:30:12 -0500
Subject: [PATCH] day17 solution

---
 day17/Makefile  |  8 ++++++++
 day17/day17.erl | 22 ++++++++++++++++++++++
 2 files changed, 30 insertions(+)
 create mode 100644 day17/Makefile
 create mode 100644 day17/day17.erl

diff --git a/day17/Makefile b/day17/Makefile
new file mode 100644
index 0000000..bc4f621
--- /dev/null
+++ b/day17/Makefile
@@ -0,0 +1,8 @@
+all: day17.beam
+	erl -noshell -s day17 start -s init stop
+
+day17.beam:
+	erlc day17.erl
+
+clean:
+	rm -f day17.beam
diff --git a/day17/day17.erl b/day17/day17.erl
new file mode 100644
index 0000000..056f85c
--- /dev/null
+++ b/day17/day17.erl
@@ -0,0 +1,22 @@
+-module(day17).
+-export([start/0]).
+
+spin_the_lock(NextValue, SpinQueue, Index, _Steps)
+  when NextValue == 2018 -> lists:nth(Index + 1 rem 2018, SpinQueue);
+spin_the_lock(NextValue, SpinQueue, Index, Steps)
+  -> NextPosition = (Index + Steps) rem NextValue,
+     { First, Last } = lists:split(NextPosition, SpinQueue),
+     spin_the_lock(NextValue + 1, lists:append([First, [NextValue], Last]), NextPosition + 1, Steps).
+
+spin_the_lock2(NextValue, ValAtOne, _Index, _Steps)
+  when NextValue == 50000001 -> ValAtOne;
+spin_the_lock2(NextValue, ValAtOne, Index, Steps)
+  -> NextPosition = (Index + Steps) rem NextValue,
+     if NextPosition == 0 -> spin_the_lock2(NextValue + 1, NextValue, NextPosition + 1, Steps);
+        true -> spin_the_lock2(NextValue + 1, ValAtOne, NextPosition + 1, Steps)
+     end.
+
+start()
+  -> io:fwrite("~p~n", [spin_the_lock(1, [0], 0, 3)]),
+     io:fwrite("~p~n", [spin_the_lock(1, [0], 0, 303)]),
+     io:fwrite("~p~n", [spin_the_lock2(1, 0, 0, 303)]).