Day 04

data/examples/04.txt

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

src/bin/04.rs

@@ -0,0 +1,108 @@
+advent_of_code::solution!(4);
+
+const DIRECTIONS: [(isize, isize); 8] = [
+    (0, 1),
+    (1, 0),
+    (1, 1),
+    (1, -1),
+    (0, -1),
+    (-1, 0),
+    (-1, -1),
+    (-1, 1),
+];
+
+fn count_xmas_occurrences(grid: Vec<Vec<char>>, target: &str) -> usize {
+    let rows = grid.len();
+    let cols = grid.len();
+    let mut count = 0;
+
+    for i in 0..rows {
+        for j in 0..cols {
+            for &(dx, dy) in &DIRECTIONS {
+                count += check_direction(&grid, i, j, dx, dy, target);
+            }
+        }
+    }
+
+    count
+}
+
+fn check_direction(
+    grid: &[Vec<char>], //&Vec<Vec<char>>,
+    start_x: usize,
+    start_y: usize,
+    dx: isize,
+    dy: isize,
+    target: &str,
+) -> usize {
+    let mut x = start_x as isize;
+    let mut y = start_y as isize;
+    let target_len = target.len();
+    let mut chars = Vec::new();
+
+    for _ in 0..target_len {
+        // Check we are within table
+        if x < 0 || y < 0 || x >= grid.len() as isize || y >= grid[0].len() as isize {
+            return 0;
+        }
+        chars.push(grid[x as usize][y as usize]);
+        x += dx;
+        y += dy;
+    }
+
+    if chars.iter().collect::<String>() == target {
+        return 1;
+    }
+
+    0
+}
+
+pub fn part_one(input: &str) -> Option<u32> {
+    let chars = input.lines().map(|line| line.chars().collect()).collect();
+    let result = count_xmas_occurrences(chars, "XMAS");
+
+    Some(result as u32)
+}
+
+pub fn part_two(input: &str) -> Option<u32> {
+    let grid = input
+        .lines()
+        .map(|l| l.chars().collect::<Vec<_>>())
+        .collect::<Vec<_>>();
+
+    let mut result: u32 = 0;
+    for i in 0..grid.len() {
+        for j in 0..grid[0].len() {
+            if grid[i][j] == 'A' && i > 0 && j > 0 && i < grid[0].len() - 1 && j < grid.len() - 1 {
+                let c1 = grid[i - 1][j - 1];
+                let c2 = grid[i + 1][j + 1];
+                let c3 = grid[i - 1][j + 1];
+                let c4 = grid[i + 1][j - 1];
+                if ((c1 == 'M' && c2 == 'S') || (c1 == 'S' && c2 == 'M'))
+                    && ((c3 == 'M' && c4 == 'S') || (c3 == 'S' && c4 == 'M'))
+                {
+                    result += 1;
+                }
+            }
+        }
+    }
+
+    Some(result)
+}
+
+#[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));
+    }
+}