From 345914c97a911932fa54ccc72dc7c2b7bb19c104 Mon Sep 17 00:00:00 2001
From: Quentin Boyer <quentin+dev@familleboyer.net>
Date: Thu, 5 Dec 2024 00:02:15 +0100
Subject: [PATCH] Day 4

---
 src/bin/day4.rs | 107 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 107 insertions(+)
 create mode 100644 src/bin/day4.rs

diff --git a/src/bin/day4.rs b/src/bin/day4.rs
new file mode 100644
index 0000000..9fa5852
--- /dev/null
+++ b/src/bin/day4.rs
@@ -0,0 +1,107 @@
+use std::time::Instant;
+
+use aoc_2024::{load, print_res};
+use bstr::{BString, ByteSlice};
+use itertools::Itertools;
+
+type Parsed<'a> = Vec<&'a [u8]>;
+
+pub fn parsing(input: &BString) -> color_eyre::Result<Parsed> {
+    Ok(input.lines().collect())
+}
+
+fn rays_index(
+    x: usize,
+    y: usize,
+    x_len: usize,
+    y_len: usize,
+    ray_length: usize,
+) -> impl Iterator<Item = impl Iterator<Item = (usize, usize)>> {
+    let x = x as isize;
+    let y = y as isize;
+    let extent = move |d, c| d * (ray_length as isize - 1) + c;
+
+    (-1..=1)
+        .filter(move |&dx| extent(dx, x) >= 0 && extent(dx, x) < x_len as isize)
+        .flat_map(move |dx| {
+            (-1..=1)
+                .filter(move |&dy| extent(dy, y) >= 0 && extent(dy, y) < y_len as isize)
+                .map(move |dy| {
+                    (0..(ray_length as isize))
+                        .map(move |n| ((x + dx * n) as usize, (y + dy * n) as usize))
+                })
+        })
+}
+
+fn rays<'a, T>(
+    x: usize,
+    y: usize,
+    table: &'a [&'a [T]],
+    ray_length: usize,
+) -> impl Iterator<Item = impl Iterator<Item = &'a T>> {
+    rays_index(x, y, table.len(), table[0].len(), ray_length)
+        .map(|ray| ray.map(|(x, y)| &table[x][y]))
+}
+
+pub fn part1(input: Parsed) {
+    let expected = b"XMAS";
+    let mut ray_count = 0;
+
+    for i in 0..input.len() {
+        for j in 0..input[0].len() {
+            let rays_at = rays(i, j, &input, expected.len())
+                .map(|ray| ray.zip_eq(expected).all(|(&a, &b)| a == b))
+                .filter(|&x| x)
+                .count();
+            ray_count += rays_at;
+        }
+    }
+
+    print_res!("Word count: {ray_count}");
+}
+
+pub fn part2(input: Parsed) {
+    let mut cross_count = 0;
+    let expected = *b"MAS";
+    let reversed = {
+        let mut ex = expected;
+        ex.reverse();
+        ex
+    };
+
+    for i in 1..(input.len() - 1) {
+        for j in 1..(input.len() - 1) {
+            let slash = [input[i - 1][j - 1], input[i][j], input[i + 1][j + 1]];
+            let backslash = [input[i - 1][j + 1], input[i][j], input[i + 1][j - 1]];
+
+            if (slash == expected || slash == reversed)
+                && (backslash == expected || backslash == reversed)
+            {
+                cross_count += 1;
+            }
+        }
+    }
+
+    print_res!("Number of 'MAS' crosses: {cross_count}");
+}
+
+pub fn main() -> color_eyre::Result<()> {
+    let context = load()?;
+
+    let start = Instant::now();
+    let parsed = parsing(&context.input)?;
+    let elapsed = humantime::format_duration(start.elapsed());
+
+    let start = Instant::now();
+    if context.part == 1 {
+        part1(parsed);
+    } else {
+        part2(parsed);
+    }
+    let elapsed_part = humantime::format_duration(start.elapsed());
+
+    println!("  Parsing: {elapsed}");
+    println!("  Solving: {elapsed_part}");
+
+    Ok(())
+}