From 5f231facc6273c655162c0713ac4ca19978e0114 Mon Sep 17 00:00:00 2001
From: Danila Fedorin <danila.fedorin@gmail.com>
Date: Fri, 11 Dec 2020 21:19:04 -0800
Subject: [PATCH] Add day 12 solution.

---
 day12.cr | 62 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 62 insertions(+)
 create mode 100644 day12.cr

diff --git a/day12.cr b/day12.cr
new file mode 100644
index 0000000..20660f0
--- /dev/null
+++ b/day12.cr
@@ -0,0 +1,62 @@
+require "advent"
+INPUT = input(2020, 12).lines.map do |l|
+  {l[0], l[1..].to_i32}
+end
+
+def part1(input)
+  pos = {0, 0}
+  angle = 0
+  input.each do |c, n|
+    case c
+    when 'N'
+      pos = pos.add({0, n})
+    when 'S'
+      pos = pos.add({0, -n})
+    when 'E'
+      pos = pos.add({n, 0})
+    when 'W'
+      pos = pos.add({-n, 0})
+    when 'L'
+      angle = (angle + n) % 360
+    when 'R'
+      angle = (angle + (360-n)) % 360
+    when 'F'
+      dists = [{1, 0}, {0, 1}, {-1, 0}, {0, -1}]
+      dx, dy = dists[angle//90]
+      pos = pos.add({dx * n, dy * n})
+    end
+  end
+  pos.map(&.abs).sum
+end
+
+def part2(input)
+  pos = {10, 1}
+  spos = {0, 0}
+  angle = 0
+  input.each do |c, n|
+    case c
+    when 'N'
+      pos = pos.add({0, n})
+    when 'S'
+      pos = pos.add({0, -n})
+    when 'E'
+      pos = pos.add({n, 0})
+    when 'W'
+      pos = pos.add({-n, 0})
+    when 'L'
+      (n//90).times do
+        pos = {-pos[1], pos[0]}
+      end
+    when 'R'
+      (n//90).times do
+        pos = {pos[1], -pos[0]}
+      end
+    when 'F'
+      spos = spos.add({pos[0] * n, pos[1]*n})
+    end
+  end
+  spos.map(&.abs).sum
+end
+
+puts part1(INPUT.clone)
+puts part2(INPUT.clone)