solution: day 4

data/examples/04.txt

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

src/bin/04.rs

@@ -0,0 +1,85 @@
+use itertools::Itertools;
+
+pub fn part_one(input: &str) -> Option<u32> {
+    let g = input.lines().map(|x| x.chars().collect_vec()).collect_vec();
+
+    #[rustfmt::skip]
+    let dirs = [
+        (1, 0), (1, 1), (0, 1), (-1, 1),
+        (-1, 0), (-1, -1), (0, -1), (1, -1),
+    ];
+    let xmas = ['X', 'M', 'A', 'S'];
+    let mut count = 0;
+
+    for (i, row) in g.iter().enumerate() {
+        for (j, _) in row.iter().enumerate() {
+            for &(di, dj) in &dirs {
+                let found_xmas = (0..4).all(|x| {
+                    let ni = i.wrapping_add((di * x) as usize);
+                    let nj = j.wrapping_add((dj * x) as usize);
+
+                    g.get(ni)
+                        .and_then(|y| y.get(nj))
+                        .copied()
+                        .unwrap_or_default()
+                        == xmas[x as usize]
+                });
+
+                if found_xmas {
+                    count += 1;
+                }
+            }
+        }
+    }
+
+    count.into()
+}
+
+pub fn part_two(input: &str) -> Option<u32> {
+    let g = input.lines().map(|x| x.chars().collect_vec()).collect_vec();
+
+    let dirs = [[(-1, -1), (0, 0), (1, 1)], [(1, -1), (0, 0), (-1, 1)]];
+    let x_mas = [['M', 'A', 'S'], ['S', 'A', 'M']];
+    let mut count = 0;
+
+    for (i, row) in g.iter().enumerate() {
+        for (j, _) in row.iter().enumerate() {
+            let found_x_mas = dirs.iter().all(|d| {
+                let s = d.iter().map(|&(di, dj)| {
+                    let ni = i.wrapping_add(di as usize);
+                    let nj = j.wrapping_add(dj as usize);
+
+                    g.get(ni)
+                        .and_then(|y| y.get(nj))
+                        .copied()
+                        .unwrap_or_default()
+                });
+
+                x_mas
+                    .iter()
+                    .any(|x| x.iter().copied().zip(s.clone()).all(|(a, b)| a == b))
+            });
+
+            if found_x_mas {
+                count += 1
+            }
+        }
+    }
+
+    count.into()
+}
+
+aoc::solution!(4);
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    #[test]
+    fn test_part_one() {
+        assert_eq!(part_one(&aoc::template::read_file("examples", 4)), Some(18));
+    }
+    #[test]
+    fn test_part_two() {
+        assert_eq!(part_two(&aoc::template::read_file("examples", 4)), Some(9));
+    }
+}