From 479affa4cc4fa896e297fe02de6ce571428e421c Mon Sep 17 00:00:00 2001
From: Danila Fedorin <danila.fedorin@gmail.com>
Date: Fri, 11 Dec 2020 11:32:33 -0800
Subject: [PATCH] Add solutions to days 10 and 11

---
 day10.cr | 37 ++++++++++++++++++++++++++++++++
 day11.cr | 64 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 101 insertions(+)
 create mode 100644 day10.cr
 create mode 100644 day11.cr

diff --git a/day10.cr b/day10.cr
new file mode 100644
index 0000000..698c1fd
--- /dev/null
+++ b/day10.cr
@@ -0,0 +1,37 @@
+require "advent"
+INPUT = input(2020, 10).lines.map(&.to_i32).sort!
+
+def part1(input)
+  diff_1 = 0
+  diff_3 = 0
+  curr = 0
+  input << (input.max + 3)
+  input.each do |i|
+    diff_1 += 1 if (i - curr) == 1
+    diff_3 += 1 if (i - curr) == 3
+    curr = i
+  end
+  puts diff_1 * diff_3
+end
+
+def count_ways(input, prev, index, mem, indent = 0)
+  if m = mem[{prev, index}]?
+    return m 
+  end
+  return 0_i64 if input[index] - prev > 3 || index >= input.size
+  return 1_i64 if index == input.size - 1
+
+  total = count_ways(input, input[index], index+1, mem, indent + 1)
+  total += count_ways(input, prev, index+1, mem, indent + 1)
+
+  mem[{prev, index}] = total
+  return total
+end
+
+def part2(input)
+  input << (input.max + 3)
+  count_ways(input, 0, 0, {} of {Int32, Int32} => Int64)
+end
+
+puts part1(INPUT.clone)
+puts part2(INPUT.clone)
diff --git a/day11.cr b/day11.cr
new file mode 100644
index 0000000..e81fca4
--- /dev/null
+++ b/day11.cr
@@ -0,0 +1,64 @@
+require "advent"
+INPUT = input(2020, 11).lines.map(&.chars) 
+
+abstract class Search
+  def search(current, x, y, dx, dy)
+    x, y = x + dx, y + dy
+    return 0 if y < 0 || y >= current.size
+    return 0 if x < 0 || x >= current[y].size
+    search_impl(current,x,y,dx,dy)
+  end
+
+  abstract def search_impl(current, x, y, dx, dy)
+end
+
+class FirstSearch < Search
+  def search_impl(current, x, y, dx, dy)
+    return current[y][x] == '#' ? 1 : 0
+  end
+end
+
+class SecondSearch < Search
+  def search_impl(current, x, y, dx, dy)
+    return 1 if current[y][x] == '#'
+    return 0 if current[y][x] == 'L'
+    return search(current, x, y, dx, dy)
+  end
+end
+
+DIRS = [{-1,-1}, {-1, 0}, {-1, 1}, {0, -1}, {0, 1}, {1, -1}, {1, 0}, {1,1}]
+
+def step(current, step, check, n)
+  current.each_with_index do |row, y|
+    row.each_with_index do |seat, x|
+      step[y][x] = current[y][x]
+      count = DIRS.sum do |dx, dy|
+        check.search(current, x, y, dx, dy)
+      end
+      step[y][x] = 'L' if seat == '#' && count >= n
+      step[y][x] = '#' if seat == 'L' && count == 0
+    end
+  end
+  {step, current}
+end
+
+def run(input, search, n)
+  current = input
+  step = input.clone
+  loop do
+    current, step = step(current, step, search, n)
+    break if current.zip_with(step) { |l, r| l == r }.all?
+  end
+  current.sum(&.count(&.==('#')))
+end
+
+def part1(input)
+  run(input, FirstSearch.new, 4)
+end
+
+def part2(input)
+  run(input, SecondSearch.new, 5)
+end
+
+puts part1(INPUT.clone)
+puts part2(INPUT.clone)