AoC20/lib/day14/day14.ex

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Elixir
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2020-12-14 17:54:29 +00:00
defmodule Day14 do
use Bitwise
@example """
mask = XXXXXXXXXXXXXXXXXXXXXXXXXXXXX1XXXX0X
mem[8] = 11
mem[7] = 101
mem[8] = 0
"""
@example2 """
mask = 000000000000000000000000000000X1001X
mem[42] = 100
mask = 00000000000000000000000000000000X0XX
mem[26] = 1
"""
def part1(example \\ false) do
parse_input(example)
|> set_mem_values()
|> Map.values()
|> Enum.sum()
end
def part2(example \\ false) do
parse_input(example)
|> set_v2_mem_values()
|> Map.values()
|> Enum.sum()
end
def parse_input(example) do
case example do
true -> @example
1 -> @example
2 -> @example2
_ -> File.read!("lib/day14/input.txt")
end
|> String.trim()
|> String.split("\n")
|> Enum.map(fn
"mask = " <> mask ->
String.to_charlist(mask)
line ->
[_, address, value] = Regex.run(~r/^mem\[(\d+)\] = (\d+)$/, line)
{String.to_integer(address), String.to_integer(value)}
end)
end
def set_mem_values(instructions, mask \\ nil, map \\ %{})
def set_mem_values([], _, map) do
map
end
def set_mem_values([new_mask | rest], _, map) when is_list(new_mask) do
set_mem_values(rest, new_mask, map)
end
def set_mem_values([{address, value} | rest], mask, map) when not is_nil(mask) do
masked_value = get_masked_value(mask, value)
set_mem_values(rest, mask, Map.put(map, address, masked_value))
end
def get_masked_value(mask, value) do
mask
|> Enum.reverse()
|> Enum.with_index()
|> Enum.reduce(value, fn {mask_val, mask_index}, value ->
case mask_val do
?X ->
value
?0 ->
value &&& bnot(1 <<< mask_index)
?1 ->
value ||| 1 <<< mask_index
end
end)
end
def set_v2_mem_values(instructions, mask \\ nil, map \\ %{})
def set_v2_mem_values([], _, map) do
map
end
def set_v2_mem_values([new_mask | rest], _, map) when is_list(new_mask) do
set_v2_mem_values(rest, new_mask, map)
end
def set_v2_mem_values([{address, value} | rest], mask, map) when not is_nil(mask) do
new_map =
calculate_all_addresses(address, mask)
# |> IO.inspect()
|> Enum.reduce(map, fn addr, map ->
Map.put(map, addr, value)
end)
set_v2_mem_values(rest, mask, new_map)
end
def calculate_all_addresses(base_addr, mask) do
base_addr
|> Integer.to_string(2)
|> String.pad_leading(length(mask), "0")
|> String.to_charlist()
|> Enum.zip(mask)
|> Enum.map(fn
{c, ?0} -> c
{_, ?1} -> ?1
{_, ?X} -> ?X
end)
|> expand_mask()
|> Enum.map(fn addr ->
addr |> List.to_string() |> String.to_integer(2)
end)
end
def expand_mask([]) do
[[]]
end
def expand_mask([?X | rest]) do
rest_expanded = expand_mask(rest)
zero = Enum.map(rest_expanded, fn mask -> [?0 | mask] end)
one = Enum.map(rest_expanded, fn mask -> [?1 | mask] end)
zero ++ one
end
def expand_mask([c | rest]) do
rest
|> expand_mask()
|> Enum.map(fn mask -> [c | mask] end)
end
end