P.S. 0x434C49434B is hexadecimal for CLICK.
adamu
derheap
Late to the game. Here is part 1. Learned the difference between mod/2 and Integer.mod/2 aka. floored modulo.
defmodule P1 do
@start 50
@positions 100
def to_rotation(text) do
dir = String.slice(text, 0..0)
# Remember to look at the input data!
number = String.slice(text, 1..9) |> String.to_integer()
{dir, number}
end
def do_rotation({dir, number}, {pos, count}) do
delta = Integer.mod(number,@positions )
new_pos =
case dir do
"L" -> Integer.mod(pos - delta, @positions )
"R" -> Integer.mod(pos + number, @positions )
end
{new_pos, if(new_pos == 0, do: count + 1, else: count)}
end
def run(input) do
{_, count} =
input
|> AOC.split_lines()
|> Enum.map(&to_rotation/1)
|> Enum.reduce({@start, 0}, fn value, acc -> do_rotation(value,acc) end)
count
end
end
0
derheap
And part 2.
defmodule P2 do
@start 50
@positions 100
def turn("L", pos, delta),
# Account for starting point zero
do:
{Integer.mod(pos - delta, @positions), if(pos != 0 && pos - delta < 0, do: 1, else: 0)}
def turn("R", pos, delta),
do: {Integer.mod(pos + delta, @positions), if(pos + delta > @positions, do: 1, else: 0)}
def do_rotation({dir, number}, {pos, count}) do
full_rotations = floor(number / @positions)
{new_pos, cross_zero} = turn(dir, pos, Integer.mod(number, @positions))
# Account for ending point zero
rotations =
count + cross_zero + full_rotations +
if(new_pos == 0,
do: 1,
else: 0
)
{new_pos, rotations}
end
def run(input) do
{_, count} =
input
|> AOC.split_lines()
|> Enum.map(&P1.to_rotation/1)
|> Enum.reduce({@start, 0}, fn value, acc -> do_rotation(value, acc) end)
count
end
end
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