From 8cb53d40617c7c66cfe4cb0572c64215c2195d3e Mon Sep 17 00:00:00 2001
From: Andrew Coleman <penguincoder@gmail.com>
Date: Mon, 4 Dec 2017 00:02:10 -0500
Subject: [PATCH] day3 solution

---
 day3/Makefile |  8 ++++++++
 day3/day3.erl | 42 ++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 50 insertions(+)
 create mode 100644 day3/Makefile
 create mode 100644 day3/day3.erl

diff --git a/day3/Makefile b/day3/Makefile
new file mode 100644
index 0000000..ece3ad8
--- /dev/null
+++ b/day3/Makefile
@@ -0,0 +1,8 @@
+all: day3.beam
+	erl -noshell -s day3 start -s init stop
+
+day3.beam:
+	erlc day3.erl
+
+clean:
+	rm -f day3.beam
diff --git a/day3/day3.erl b/day3/day3.erl
new file mode 100644
index 0000000..021b0a0
--- /dev/null
+++ b/day3/day3.erl
@@ -0,0 +1,42 @@
+-module(day3).
+-export([start/0]).
+
+next_largest_square(Target)
+  -> recurse_next_largest_square(1, Target).
+
+recurse_next_largest_square(X, Target)
+  when (X rem 2) =/= 0, (X*X) >= Target -> X;
+recurse_next_largest_square(X, Target)
+  -> recurse_next_largest_square(X+1, Target).
+
+position_in_outer_shell(Square, Target)
+  -> PreviousSquare = (Square - 2) * (Square - 2),
+     Target - PreviousSquare.
+
+position_on_side(Position, Square)
+  when Position == 0 -> Square - 1;
+position_on_side(_Position, Square)
+  when Square == 1 -> 1;
+position_on_side(Position, Square)
+  -> Offset = Position rem (Square - 1),
+     if Offset == 0 -> Square - 1;
+               true -> Offset end.
+
+distance_to_center(Position, Square)
+  -> Center = Square div 2,
+     VertOffset = abs(Center - Position),
+     Center + VertOffset.
+
+find_distance(Target)
+  -> Square = next_largest_square(Target),
+     Position = position_in_outer_shell(Square, Target),
+     Index = position_on_side(Position, Square),
+     distance_to_center(Index, Square).
+
+start()
+  -> io:fwrite("~B ~B~n", [1, find_distance(1)]),
+     io:fwrite("~B ~B~n", [12, find_distance(12)]),
+     io:fwrite("~B ~B~n", [23, find_distance(23)]),
+     io:fwrite("~B ~B~n", [1024, find_distance(1024)]),
+     io:fwrite("~B ~B~n", [368078, find_distance(368078)]),
+     io:fwrite("https://oeis.org/A141481/b141481.txt~n").