From 53977edeadd2df1074d472bcb7022f77b5011ce0 Mon Sep 17 00:00:00 2001
From: Daniel Lin <ephemient@gmail.com>
Date: Wed, 4 Dec 2024 10:43:11 -0500
Subject: [PATCH] Extract constants

---
 rs/Cargo.lock  | 16 ++++++++++++++++
 rs/Cargo.toml  |  1 +
 rs/src/day4.rs | 23 ++++++++++++-----------
 3 files changed, 29 insertions(+), 11 deletions(-)

diff --git a/rs/Cargo.lock b/rs/Cargo.lock
index 57b6ac25..b16a1937 100644
--- a/rs/Cargo.lock
+++ b/rs/Cargo.lock
@@ -27,12 +27,28 @@ checksum = "55cc3b69f167a1ef2e161439aa98aed94e6028e5f9a59be9a6ffb47aef1651f9"
 name = "aoc2024"
 version = "0.1.0"
 dependencies = [
+ "array-util",
  "criterion",
  "indoc",
  "itertools 0.13.0",
  "pretty_assertions",
 ]
 
+[[package]]
+name = "array-util"
+version = "1.0.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7e509844de8f09b90a2c3444684a2b6695f4071360e13d2fda0af9f749cc2ed6"
+dependencies = [
+ "arrayvec",
+]
+
+[[package]]
+name = "arrayvec"
+version = "0.7.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7c02d123df017efcdfbd739ef81735b36c5ba83ec3c59c80a9d7ecc718f92e50"
+
 [[package]]
 name = "autocfg"
 version = "1.4.0"
diff --git a/rs/Cargo.toml b/rs/Cargo.toml
index d2bc545c..e105df58 100644
--- a/rs/Cargo.toml
+++ b/rs/Cargo.toml
@@ -17,6 +17,7 @@ name = "aoc2024"
 path = "src/main.rs"
 
 [dependencies]
+array-util = "1.0.2"
 itertools = "0.13"
 
 [dev-dependencies]
diff --git a/rs/src/day4.rs b/rs/src/day4.rs
index ce595f2f..a7585e09 100644
--- a/rs/src/day4.rs
+++ b/rs/src/day4.rs
@@ -1,29 +1,34 @@
+use array_util::try_from_fn;
 use itertools::izip;
 
 pub fn part1(data: &str) -> usize {
+    const XMAS: [[u8; 4]; 2] = [*b"XMAS", *b"SAMX"];
+
     let lines = &data.lines().collect::<Vec<_>>()[..];
     lines
         .iter()
         .enumerate()
         .flat_map(|(y, line)| {
             (0..line.len()).flat_map(move |x| {
-                (-1..=1).flat_map(move |dy| {
-                    (-1..=1).filter(move |dx| {
-                        "XMAS".bytes().enumerate().all(|(i, b)| {
+                [(1, 0), (1, 1), (0, 1), (-1, 1)]
+                    .iter()
+                    .filter_map(move |(dx, dy)| {
+                        try_from_fn(|i| {
                             y.checked_add_signed(i as isize * dy)
                                 .and_then(|y| lines.get(y))
                                 .zip(x.checked_add_signed(i as isize * dx))
-                                .and_then(|(line, x)| line.as_bytes().get(x))
-                                == Some(&b)
+                                .and_then(|(line, x)| line.as_bytes().get(x).copied())
                         })
                     })
-                })
             })
         })
+        .filter(|s| XMAS.contains(s))
         .count()
 }
 
 pub fn part2(data: &str) -> usize {
+    const XMAS: [[u8; 5]; 4] = [*b"MMASS", *b"MSAMS", *b"SMASM", *b"SSAMM"];
+
     let lines = data.lines().collect::<Vec<_>>();
     izip!(&lines[..], &lines[1..], &lines[2..])
         .flat_map(|(above, line, below)| {
@@ -34,12 +39,8 @@ pub fn part2(data: &str) -> usize {
                 below.bytes(),
                 below.bytes().skip(2)
             )
-            .filter(|&(nw, ne, b, sw, se)| {
-                b == b'A'
-                    && (nw == b'M' && se == b'S' || se == b'M' && nw == b'S')
-                    && (ne == b'M' && sw == b'S' || sw == b'M' && ne == b'S')
-            })
         })
+        .filter(|&(nw, ne, b, sw, se)| XMAS.contains(&[nw, ne, b, sw, se]))
         .count()
 }