defmodule Day10 do
def part1(data) do
grid = data
|> String.split("\n", trim: true)
|> Enum.map(&String.codepoints/1)
|> Enum.map(fn v -> Enum.map(v, &String.to_integer/1) end)
values = for {l, i} <- Enum.with_index(grid),
{v, j} <- Enum.with_index(l) do
{v, {i, j}}
end
|> Enum.group_by(fn {v, _} -> v end, fn {_, p} -> p end)
dist = fn {a, b}, {c, d} -> abs(a-c) + abs(b-d) end
ends = fn p, prev ->
for {_, v} <- Enum.filter(prev, fn {p2, _} -> dist.(p, p2) == 1 end),
reduce: MapSet.new() do
acc -> MapSet.union(acc, v)
end
end
for i <- 8..0//-1,
reduce: Map.get(values, 9, []) |> Enum.map(& {&1, MapSet.new([&1])}) do
acc -> Map.get(values, i, [])
|> Enum.map(fn p -> {p, ends.(p, acc)} end)
|> Enum.filter(fn {_, m} -> MapSet.size(m) > 0 end)
end
|> Enum.map(fn {_, m} -> MapSet.size(m) end)
|> Enum.sum()
end
def part2(data) do
grid = data
|> String.split("\n", trim: true)
|> Enum.map(&String.codepoints/1)
|> Enum.map(fn v -> Enum.map(v, &String.to_integer/1) end)
values = for {l, i} <- Enum.with_index(grid),
{v, j} <- Enum.with_index(l) do
{v, {i, j}}
end
|> Enum.group_by(fn {v, _} -> v end, fn {_, p} -> p end)
acc = values
|> Map.get(9, [])
|> Enum.map(fn p -> {p, 1} end)
dist = fn {a, b}, {c, d} -> abs(a-c) + abs(b-d) end
count = fn p, prev ->
prev
|> Enum.filter(fn {p2, _} -> dist.(p, p2) == 1 end)
|> Enum.map(fn {_, c} -> c end)
|> Enum.sum()
end
for i <- 8..0//-1, reduce: acc do
acc -> Map.get(values, i, [])
|> Enum.map(fn p -> {p, count.(p, acc)} end)
|> Enum.filter(fn {_, c} -> c > 0 end)
end
|> Enum.map(fn {_, c} -> c end)
|> Enum.sum()
end
end
data = IO.read(:stdio, :eof)
{time1 , ans1} = :timer.tc(fn -> Day10.part1(data) end)
IO.puts("Time : #{time1 / 1000000}")
IO.puts("Answer: #{ans1}")
{time2 , ans2} = :timer.tc(fn -> Day10.part2(data) end)
IO.puts("Time : #{time2 / 1000000}")
IO.puts("Answer: #{ans2}")
