Is this run through the list even needed? (if so you could always just make this part of parse/1, just curious)
I can’t believe I have been doing this for this long without knowing about binary_part/3 - thanks!
srowley
0
Aetherus
The <<^char <- pass>> part is cool! Thank you for showing me another thing in Elixir that I don’t know 
1
ricardo-h
O(mn) solution.
solution 1
defmodule Advent.Day2 do
import String, only: [split: 2, to_integer: 1, at: 2]
def start(part, file \\ "/tmp/data.txt") do
File.read!(file)
|> String.split("\n")
|> Enum.reduce(0, fn line, acc -> acc + is_valid(line, part) end)
end
defp is_valid(line, _part) when line in ["", nil], do: 0
defp is_valid(line, :part1) do
[min, max, letter, _, passwd] = split(line, ["-", " ", ":"])
<<word::utf8>> = letter
count = Enum.count(to_charlist(passwd), fn x -> x == word end)
((to_integer(min) <= count) and (count <= to_integer(max))) && 1 || 0
end
defp is_valid(line, :part2) do
[p1, p2, letter, _, passwd] = split(line, ["-", " ", ":"])
case {at(passwd, to_integer(p1) - 1) == letter, at(passwd, to_integer(p2) - 1) == letter} do
{true, false} -> 1
{false, true} -> 1
_ -> 0
end
end
end
antoher solution for part1
defmodule Advent.Day2b do
import String, only: [split: 2, to_integer: 1, replace: 3, at: 2]
def start(part, file \\ "/tmp/data.txt") do
File.read!(file)
|> split("\n")
|> Enum.reduce(0, fn line, acc -> acc + is_valid(line, part) end)
end
defp is_valid(line, _) when line in ["", nil], do: 0
defp is_valid(line, :part1) do
[min, max, letter, _, passwd] = split(line, ["-", " ", ":"])
count = byte_size(passwd) - byte_size(replace(passwd, letter, ""))
((to_integer(min) <= count) and (count <= to_integer(max))) && 1 || 0
end
defp is_valid(line, :part2) do
[p1, p2, letter, _, passwd] = split(line, ["-", " ", ":"])
case {at(passwd, to_integer(p1) - 1) == letter, at(passwd, to_integer(p2) - 1) == letter} do
{true, false} -> 1
{false, true} -> 1
_ -> 0
end
end
end
1
Hanspagh
What is the benefit of duing
over something like
pass
|> String.codepoints()
|> Enum.count(& &1 == char)
1
hauleth
Codepoints is slower as it needs to understand UTF-8 encoding. Mine is just passing over all bytes in the binary. Also mine does everything in one pass instead of 2 passes (one pass over the binary to construct list and another over the list to count occurrences). Not that this matter in this case, but I didn’t wanted to do 2 passes.
1
romenigld
I was trying this today, but for take the total in the final I was unable.
someone could help me with this?
trying this
defmodule Day2 do
@type claim :: String.t
@type parsed_claim :: list
@spec parse_claim(binary) :: :ok
@moduledoc """
Advent of Code `Day2`.
"""
def values do
values =
File.read!("lib/input.txt")
|> String.trim()
|> String.split("\n")
|> Enum.map(&parse_claim/1)
end
@spec parse_claim(claim) :: parsed_claim
def parse_claim(string) when is_binary(string) do
string
|> String.split(["-", " ", ":", " "], trim: true)
|> claimed_values()
end
def claimed_values(parsed_claims) do
[min, max, char_str, str] = parsed_claims
r_min = String.to_integer(min)
r_max = String.to_integer(max)
#validate password
if str |> String.contains?(char_str) do
char_key = take_char(char_str)
list_char = take_char(str)
calculate_password([r_min, r_max, char_key, list_char])
end
end
defp take_char(char) do
char
|> String.graphemes
|> Enum.map(&String.to_charlist/1)
end
defp calculate_password([min, max, char_key, list_char]) do
count = Enum.count(list_char, &(&1 == char_key))
if ((count >= min) && (count <= max)), do: total + 1, else: total
end
end
0
Aetherus
Sorry for being late (I was sleeping).
I’m trying your solution, and the first error I found is in this function:
defp calculate_password([min, max, char_key, list_char]) do
count = Enum.count(list_char, &(&1 == char_key))
if ((count >= min) && (count <= max)), do: total + 1, else: total
# ^^^^^ ^^^^^
end
The variable total is not defined. If you want a global variable, well, there’s no variable variables of any kind in Elixir. So, you have to use some kind of reduce.
UPDATE 1
The take_char/1 function doesn’t make sense to me. It returns a list of lists with each sub-list contains only 1 integer (the codepoint of the character). I think the |> Enum.map(&String.to_charlist/1) can be dropped. By the way, you can directly compare to strings/binaries without converting them to charlists.
0
romenigld
Thank you for your reply Aetherus:
I realized doing this:
defmodule Day2 do
@moduledoc """
Advent of Code `Day2`.
"""
def run do
File.read!("lib/input.txt")
|> String.split("\n", trim: true)
|> Enum.map(&parse_claim/1)
end
@doc """
Reads the file and execute the logic and returns the result
## Examples
iex> Day2.values
636
"""
def part1 do
run()
|> Enum.map(fn [min, max, key, password] ->
check_part1?(String.to_integer(min), String.to_integer(max), key, password)
end)
|> Enum.count(&(&1))
end
def part2 do
run()
|> Enum.map(fn [min, max, key, password] ->
check_part2?(String.to_integer(min), String.to_integer(max), key, password)
end)
|> Enum.count(&(&1))
end
@doc """
Parses a claim.
## Examples
iex> Day2.parse_claim("1-3 a: abcde")
["1", "3", "a", "abcde"]
"""
def parse_claim(list_string) when is_binary(list_string) do
list_string
|> String.split(["-", " ", ":", " "], trim: true) # ["1", "3", "p", "pppp"], [...]
end
defp check_part1?(r_min, r_max, key, password) do
if String.contains?(password, key) do
count =
password
|> String.graphemes
|> Enum.filter(fn x -> x == key end)
|> Enum.count
#count >= r_min && count <= r_max
count in r_min..r_max
end
end
defp check_part2?(r_min, r_max, key, password) do
if String.contains?(password, key) do
list =
password
|> String.graphemes
x_min = list |> Enum.at(r_min - 1) == key
x_max = list |> Enum.at(r_max - 1) == key
x_min != x_max
end
end
end
1
Rainer
My approach, as I started learning Erlang… 
-module(day2).
-export([run/0]).
run()->
ParsedLines = load_file("day2input.txt"),
{part1(ParsedLines), part2(ParsedLines)}.
part1(ParsedLines)->
ValidLines = [ Line || Line <- ParsedLines, is_valid1(Line)],
length(ValidLines).
part2(ParsedLines)->
ValidLines = [ Line || Line <- ParsedLines, is_valid2(Line)],
length(ValidLines).
is_valid1({From, To, Char, Pw}) ->
N = length([[X] || X <- Pw, [X] =:= Char]),
(N >= From) and (N =< To).
is_valid2({Idx1, Idx2, Char, Pw}) ->
(string:slice(Pw, Idx1-1, 1) =:= Char) xor (string:slice(Pw, Idx2-1, 1) =:= Char).
load_file(Filename)->
{ok, Binary} = file:read_file(Filename),
StringContent = unicode:characters_to_list(Binary),
[ parse(Line) || Line <- string:tokens(StringContent, "\n")].
parse(Line)->
{ok, MP} = re:compile("([0-9]+)-([0-9]+) ([a-z]): ([a-z]+)"),
{_,[_,From, To, Char, Pw]} = re:run(Line, MP),
{extract_num(Line, From), extract_num(Line, To), extract_str(Line, Char), extract_str(Line, Pw)}.
extract_str(String, {Start, End})->
string:slice(String, Start, End).
extract_num(String, {Start, End})->
Str = string:slice(String, Start, End),
{Int, _} = string:to_integer(Str),
Int.
For part 1 I did a list comprehension on the string to get the number of occurrences.
3
Sanjibukai
For the first part I did the following knowing that splitting a string with non-existing character leave the string itself and if it’s present n times it gives n+1 chunks:
defp valid?({range, letter, password}) do
chunks =
password
|> String.split(letter)
|> Enum.count()
(chunks - 1) in range
end
1