AOC 2024 Day 04

Author: raul-sauco

aoc/2024/rust/Cargo.lock

@@ -24,6 +24,7 @@ test_lib = []
 # Template dependencies
 chrono = { version = "0.4.38", optional = true }
 dhat = { version = "0.3.3", optional = true }
+glam = "0.29.2"
 itertools = "0.13.0"
 pico-args = "0.5.0"
 regex = "1.11.1"

aoc/2024/rust/Cargo.toml

@@ -0,0 +1,10 @@
+MMMSXXMASM
+MSAMXMSMSA
+AMXSXMAAMM
+MSAMASMSMX
+XMASAMXAMM
+XXAMMXXAMA
+SMSMSASXSS
+SAXAMASAAA
+MAMMMXMMMM
+MXMXAXMASX

aoc/2024/rust/data/examples/04.txt

@@ -0,0 +1,141 @@
+advent_of_code::solution!(4);
+
+use glam::{i32, IVec2};
+use std::collections::HashMap;
+
+/**
+ * Display the 9 characters in the matrix centered around the given position.
+*/
+#[allow(dead_code)]
+fn get_graph(matrix: &HashMap<IVec2, char>, pos: &IVec2) -> String {
+    let mut graph = String::with_capacity(12);
+    for y in -1..=1 {
+        for x in -1..=1 {
+            let offset = IVec2::new(x, y);
+            if let Some(char) = matrix.get(&(*pos + offset)) {
+                graph.push(*char);
+            } else {
+                graph.push('.');
+            }
+        }
+        graph.push('\n');
+    }
+    graph
+}
+
+fn parse(input: &str) -> HashMap<IVec2, char> {
+    let mut grid = HashMap::new();
+    for (y, line) in input.lines().enumerate() {
+        for (x, char) in line.chars().enumerate() {
+            grid.insert(
+                IVec2 {
+                    x: x as i32,
+                    y: y as i32,
+                },
+                char,
+            );
+        }
+    }
+    grid
+}
+
+/* ********************************** PART ONE *******************************/
+
+const DIRECTIONS: [IVec2; 8] = [
+    IVec2::new(0, -1),
+    IVec2::new(0, 1),
+    IVec2::new(-1, 0),
+    IVec2::new(1, 0),
+    IVec2::new(-1, -1),
+    IVec2::new(1, -1),
+    IVec2::new(-1, 1),
+    IVec2::new(1, 1),
+];
+
+fn find_xmas(matrix: &HashMap<IVec2, char>, pos: IVec2) -> u32 {
+    let target = "XMAS";
+    let mut res = 0;
+    let mut is_match;
+    for dir in DIRECTIONS {
+        is_match = true;
+        for (i, c) in target.chars().enumerate() {
+            if let Some(cell) = matrix.get(&(pos + dir * i as i32)) {
+                if *cell != c {
+                    is_match = false;
+                    break;
+                }
+            } else {
+                is_match = false;
+                break;
+            }
+        }
+        if is_match {
+            res += 1;
+        }
+    }
+    res
+}
+
+pub fn part_one(input: &str) -> Option<u32> {
+    let matrix = parse(input);
+    Some(matrix.keys().map(|k| find_xmas(&matrix, *k)).sum::<u32>())
+}
+
+/* ********************************** PART TWO *******************************/
+
+const DIRECTIONS_X: [[IVec2; 2]; 2] = [
+    [IVec2::new(-1, -1), IVec2::new(1, 1)],
+    [IVec2::new(-1, 1), IVec2::new(1, -1)],
+];
+
+/**
+* Find if the given coordinates in the matrix are at the center of a X-MAs group of cells, for that
+* to be true, both diagonals need to form "MAS" or "SAM", given that main will call this method
+* only when the char at pos is 'A', we only need to check that the oppossing corners are either SM
+* or MS.
+*/
+fn is_x_mas_match(matrix: &HashMap<IVec2, char>, pos: &IVec2) -> bool {
+    let (ms, sm) = ("MS".to_string(), "SM".to_string());
+    let mut diagonal_chars = String::with_capacity(2);
+    for diagonal in DIRECTIONS_X {
+        diagonal_chars.clear();
+        for offset in diagonal {
+            if let Some(c) = matrix.get(&(pos + offset)) {
+                diagonal_chars.push(*c);
+            } else {
+                return false;
+            }
+        }
+        if diagonal_chars != ms && diagonal_chars != sm {
+            return false;
+        }
+    }
+    true
+}
+
+pub fn part_two(input: &str) -> Option<u32> {
+    let matrix = parse(input);
+    Some(
+        matrix
+            .iter()
+            .filter(|&(pos, val)| *val == 'A' && is_x_mas_match(&matrix, pos))
+            .count() as u32,
+    )
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_part_one() {
+        let result = part_one(&advent_of_code::template::read_file("examples", DAY));
+        assert_eq!(result, Some(18));
+    }
+
+    #[test]
+    fn test_part_two() {
+        let result = part_two(&advent_of_code::template::read_file("examples", DAY));
+        assert_eq!(result, Some(9));
+    }
+}