# Day 2
## Utils
```elixir
defmodule U do
def numbers(l) do
String.split(l) |> Enum.map(&String.to_integer/1)
end
end
```
```elixir
input = File.stream!("2/example.txt") |> Stream.map(&U.numbers/1)
```
```elixir
defmodule Day2 do
def is_safe([n1, n2 | _] = l) do
is_increasing = 0 < n1 - n2
is_safe(is_increasing, l)
end
defp is_safe(_, [_]), do: true
defp is_safe(is_increasing, [p, n | tail]) do
diff = p - n
((0 < diff) == is_increasing) && (0 < abs(diff)) && (abs(diff) < 4) && is_safe(is_increasing, [n | tail])
end
end
```
```elixir
input |> Stream.filter(&Day2.is_safe/1) |> Enum.count()
```
```elixir
defmodule Day2_2 do
def is_safe(l), do: is_safe(nil, l, true)
defp is_safe(_, [_], _), do: true
defp is_safe(is_increasing, [n1, n2 | tail], can_fail) do
IO.inspect({is_increasing, n1, n2, can_fail})
if (n1 == n2) || 3 < abs(n1 - n2) do
if can_fail do
is_safe(is_increasing, [n2 | tail], false)
else
false
end
else
is_increasing = if is_increasing == nil, do: 0 < n2 - n1, else: is_increasing
if 0 < (n2 - n1) != is_increasing do
if can_fail do
is_safe(is_increasing, [n2 | tail], false)
else
false
end
else
is_safe(is_increasing, [n2 | tail], can_fail)
end
end
end
end
```
```elixir
input |> Stream.filter(&Day2_2.is_safe/1) |> Enum.count()
```
