From c14a9085410934cc45e418756ff3094c6992cc6c Mon Sep 17 00:00:00 2001
From: sloane <1699281+sloanelybutsurely@users.noreply.github.com>
Date: Sat, 9 Dec 2023 13:25:55 -0500
Subject: [PATCH] solve 2023 9.1
---
2023/README.md | 3 ++-
2023/lib/2023/9.ex | 31 ++++++++++++++++++++++
2023/lib/{AOCHelpers.ex => aoc_helpers.ex} | 17 ++++++++++++
README.md | 2 +-
4 files changed, 51 insertions(+), 2 deletions(-)
create mode 100644 2023/lib/2023/9.ex
rename 2023/lib/{AOCHelpers.ex => aoc_helpers.ex} (69%)
diff --git a/2023/README.md b/2023/README.md
index 47ecd57..8059552 100644
--- a/2023/README.md
+++ b/2023/README.md
@@ -3,7 +3,7 @@
| S | M | T | W | T | F | S |
| :-: | :-: | :-: | :-: | :-: | :-: | :-: |
| | | | | | [1] | [2] |
-| [3] | [4] | [5] | 6 | [7] | [8] | 9 |
+| [3] | [4] | [5] | 6 | [7] | [8] | [9] |
| 10 | 11 | 12 | 13 | 14 | 15 | 16 |
| 17 | 18 | 19 | 20 | 21 | 22 | 23 |
| 24 | 25 | | | | | |
@@ -17,3 +17,4 @@
<!-- [6]: ./lib/2023/6.ex -->
[7]: ./lib/2023/7.ex
[8]: ./lib/2023/8.ex
+[9]: ./lib/2023/9.ex
diff --git a/2023/lib/2023/9.ex b/2023/lib/2023/9.ex
new file mode 100644
index 0000000..01da81e
--- /dev/null
+++ b/2023/lib/2023/9.ex
@@ -0,0 +1,31 @@
+import AOC
+import AOCHelpers
+
+aoc 2023, 9 do
+ def p1(input) do
+ input
+ |> lines_of_integers()
+ |> Enum.map(&next_in_sequence/1)
+ |> Enum.sum()
+ end
+
+ def p2(_input) do
+ end
+
+ def next_in_sequence(xs) do
+ xs
+ |> differentiate()
+ |> Enum.map(&List.last/1)
+ |> Enum.sum()
+ end
+
+ def differentiate(xs) do
+ xs
+ |> Stream.iterate(&deltas/1)
+ |> Enum.take_while(&(not all_zeros?(&1)))
+ end
+
+ def deltas(xs), do: Enum.zip_with(xs, Enum.drop(xs, 1), &(&2 - &1))
+
+ def all_zeros?(xs), do: Enum.all?(xs, is?(0))
+end
diff --git a/2023/lib/AOCHelpers.ex b/2023/lib/aoc_helpers.ex
similarity index 69%
rename from 2023/lib/AOCHelpers.ex
rename to 2023/lib/aoc_helpers.ex
index b96f17e..16e0df5 100644
--- a/2023/lib/AOCHelpers.ex
+++ b/2023/lib/aoc_helpers.ex
@@ -11,6 +11,22 @@ defmodule AOCHelpers do
String.split(str, "", trim: true)
end
+ def integers(str) when is_binary(str) do
+ str
+ |> words()
+ |> integers()
+ end
+
+ def integers(ws) when is_list(ws) do
+ Enum.map(ws, &String.to_integer/1)
+ end
+
+ def lines_of_integers(input) do
+ input
+ |> lines()
+ |> Enum.map(&integers/1)
+ end
+
@doc """
Take a list of terms and a list of 1-arity functions and apply each function
to the coresponding term in the list of terms.
@@ -27,4 +43,5 @@ defmodule AOCHelpers do
def id(x), do: x
def always(x), do: fn -> x end
+ def is?(x), do: &(&1 == x)
end
diff --git a/README.md b/README.md
index d5cc989..ec67642 100644
--- a/README.md
+++ b/README.md
@@ -14,7 +14,7 @@
1. [2020] **17/50** 🌟
1. [2021] **43/50** 🌟
1. [2022] **14/50** 🌟
-1. [2023] **13/50** 🌟
+1. [2023] **14/50** 🌟
[2015]: ./2015
[2017]: ./2017