From 8f51f3914effb85f9928b7d7b2349e07a104baf5 Mon Sep 17 00:00:00 2001
From: Jordan Doyle <jordan@doyle.la>
Date: Sat, 07 Dec 2024 17:14:56 +0000
Subject: [PATCH] Add 2024 day 4

---
 Cargo.toml |   4 ++++
 README     |   4 ++--
 2024/01.rs |   1 +
 2024/04.rs | 109 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 116 insertions(+), 2 deletions(-)

diff --git a/Cargo.toml b/Cargo.toml
index 246299a..173c6d7 100644
--- a/Cargo.toml
+++ a/Cargo.toml
@@ -30,6 +30,10 @@
 name = "aoc2024-01"
 path = "2024/01.rs"
 
+[[bin]]
+name = "aoc2024-04"
+path = "2024/04.rs"
+
 [profile.release]
 overflow-checks = true
 
diff --git a/README b/README
index 5d29f89..17ee834 100644
--- a/README
+++ a/README
@@ -17,8 +17,8 @@
 |        1 | Rust     | |        1 | Haskell  | |        1 | Fortran  |
 |        2 | OCaml    | |        2 | Haskell  | |        2 | Nix      |
 |        3 | Perl     | |        3 | Haskell  | |        3 | Clojure  |
-+---------------------+ |        4 | Haskell  | |        4 | Jsonnet  |
-                        |        5 | Rust     | |        5 | HCL/TF   |
+|        4 | Rust     | |        4 | Haskell  | |        4 | Jsonnet  |
++---------------------+ |        5 | Rust     | |        5 | HCL/TF   |
                         |        6 | Haskell  | |        6 | Apache2  |
                         |        7 | Haskell  | +---------------------+
                         |        8 | Haskell  |
diff --git a/2024/01.rs b/2024/01.rs
index 36325c2..e1bd931 100644
--- a/2024/01.rs
+++ a/2024/01.rs
@@ -1,4 +1,5 @@
 #![feature(binary_heap_into_iter_sorted)]
+#![allow(clippy::cast_possible_truncation)]
 use std::{cmp::Reverse, collections::BinaryHeap, io::Read};
 
 use itertools::Itertools;
diff --git a/2024/04.rs b/2024/04.rs
new file mode 100644
index 0000000..2509859 100644
--- /dev/null
+++ a/2024/04.rs
@@ -1,0 +1,109 @@
+#![allow(clippy::cast_possible_wrap, clippy::cast_sign_loss)]
+
+use std::io::Read;
+
+use itertools::Itertools;
+
+fn main() {
+    let mut input = String::new();
+    std::io::stdin().read_to_string(&mut input).unwrap();
+    let input = input.trim();
+
+    let rows = input.lines().count();
+    let cols = input.split_once('\n').unwrap().0.len();
+
+    let input = input.replace('\n', "");
+
+    part1(&input, rows, cols);
+    part2(&input, cols);
+}
+
+fn part1(input: &str, rows: usize, cols: usize) {
+    const VARIANTS: &[[(isize, isize); 3]] = &[
+        // forward
+        [(1, 0), (2, 0), (3, 0)],
+        // backwards
+        [(-1, 0), (-2, 0), (-3, 0)],
+        // downwards
+        [(0, 1), (0, 2), (0, 3)],
+        // upwards
+        [(0, -1), (0, -2), (0, -3)],
+        // diag up left
+        [(-1, -1), (-2, -2), (-3, -3)],
+        // diag up right
+        [(1, -1), (2, -2), (3, -3)],
+        // diag down right
+        [(1, 1), (2, 2), (3, 3)],
+        // diag down left
+        [(-1, 1), (-2, 2), (-3, 3)],
+    ];
+
+    let char_at_pos = |n| &input[n..=n];
+    let mut found = 0;
+
+    let indicies = input
+        .char_indices()
+        .filter(|(_, c)| *c == 'X')
+        .collect_vec();
+
+    for (pos, _) in indicies {
+        let curr_char_row = pos / cols;
+
+        let get_at_offset = |&(x, y): &(isize, isize)| {
+            char_at_pos((pos as isize + (cols as isize * y) + x) as usize)
+        };
+
+        for [v1, v2, v3] in VARIANTS {
+            let (max_x, max_y) = v3;
+
+            // if max_x will overflow the row, or if the max_y will take us outside of the grid,
+            // skip
+            if (pos as isize + max_x) / cols as isize != curr_char_row as isize
+                || curr_char_row as isize + max_y < 0
+                || curr_char_row as isize + max_y >= rows as isize
+            {
+                continue;
+            }
+
+            if get_at_offset(v1) == "M" && get_at_offset(v2) == "A" && get_at_offset(v3) == "S" {
+                found += 1;
+            }
+        }
+    }
+
+    eprintln!("{found}");
+}
+
+fn part2(input: &str, cols: usize) {
+    let char_at_pos = |n| &input[n..=n];
+    let mut found = 0;
+
+    let indicies = input
+        .char_indices()
+        .filter(|(_, c)| *c == 'A')
+        .collect_vec();
+
+    for (pos, _) in indicies {
+        let get_at_offset =
+            |(x, y): (isize, isize)| char_at_pos((pos as isize + (cols as isize * y) + x) as usize);
+
+        if pos < cols || pos % cols < 1 || pos + cols > input.len() {
+            continue;
+        }
+
+        let top_left = get_at_offset((-1, -1));
+        let top_right = get_at_offset((1, -1));
+        let bottom_left = get_at_offset((-1, 1));
+        let bottom_right = get_at_offset((1, 1));
+
+        match (top_left, top_right, bottom_left, bottom_right) {
+            ("M", "S", "M", "S")
+            | ("S", "M", "S", "M")
+            | ("M", "M", "S", "S")
+            | ("S", "S", "M", "M") => found += 1,
+            _ => {}
+        }
+    }
+
+    eprintln!("{found}");
+}
--
rgit 0.1.5