From 6ecae2b5bf63b118252bb8992bbef59941191147 Mon Sep 17 00:00:00 2001
From: Danila Fedorin <danila.fedorin@gmail.com>
Date: Sun, 13 Dec 2020 21:53:37 -0800
Subject: [PATCH] Add day 4 solution.

---
 day14.cr | 60 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 60 insertions(+)
 create mode 100644 day14.cr

diff --git a/day14.cr b/day14.cr
new file mode 100644
index 0000000..d6fc3fe
--- /dev/null
+++ b/day14.cr
@@ -0,0 +1,60 @@
+require "advent"
+raw = input(2020, 14).lines
+input = [] of {UInt64, UInt64, Array(Int32), UInt64, UInt64}
+
+and_mask = (2_u64**63) + (2_u64**63-1)
+or_mask = 0_u64
+floats = [] of Int32
+
+raw.each do |line|
+  if data = line.match(/^mask = (.+)$/)
+    new_mask = data[1]
+    and_mask = (2_u64**63) + (2_u64**63-1)
+    or_mask = 0_u64
+    floats = [] of Int32
+    new_mask.reverse.chars.each_with_index do |c, i|
+      floats << i if c == 'X'
+      or_mask = or_mask | (1_u64 << i) if c == '1'
+      and_mask = and_mask & ~(1_u64 << i) if c == '0'
+    end
+  elsif data = line.match(/^mem\[(\d+)\] = (\d+)$/)
+    input << {and_mask, or_mask, floats, data[1].to_u64, data[2].to_u64}
+  else
+    raise "Invalid line"
+  end
+end
+
+def part1(input)
+  memory = {} of UInt64 => UInt64
+  input.each do |i|
+    and_mask, or_mask, floats, addr, v = i
+    memory[addr] = (v & and_mask) | or_mask
+  end
+  memory.values.sum
+end
+
+def generate_possible(indices, index, n, &block : UInt64 -> _)
+  if index == indices.size
+    yield n
+    return 
+  end
+  float_addr = indices[index]
+  no = n | (1_u64 << float_addr)
+  generate_possible(indices, index+1, no, &block)
+  nz = n & ~(1_u64 << float_addr)
+  generate_possible(indices, index+1, nz, &block)
+end
+
+def part2(input)
+  memory = {} of UInt64 => UInt64
+  input.each do |i|
+    _, or_mask, floats, addr, v = i
+    generate_possible(floats, 0, addr | or_mask) do |addr|
+      memory[addr] = v
+    end
+  end
+  memory.values.sum
+end
+
+puts part1(input)
+puts part2(input)