4th day

Author: majcn

data/examples/04.txt

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

src/bin/04.rs

@@ -0,0 +1,95 @@
+advent_of_code::solution!(4);
+
+use advent_of_code::maneatingape::grid::*;
+use advent_of_code::maneatingape::point::*;
+
+fn parse_data(input: &str) -> Grid<u8> {
+    Grid::parse(input)
+}
+
+pub fn part_one(input: &str) -> Option<u32> {
+    let data = parse_data(input);
+
+    const MAS: [u8; 3] = [b'M', b'A', b'S'];
+
+    let validate = |x, y, dx, dy| -> bool {
+        if !data.contains(Point::new(x + 3 * dx, y + 3 * dy)) {
+            return false;
+        }
+
+        let a = [
+            data[Point::new(x + dx, y + dy)],
+            data[Point::new(x + 2 * dx, y + 2 * dy)],
+            data[Point::new(x + 3 * dx, y + 3 * dy)],
+        ];
+
+        a == MAS
+    };
+
+    let mut result = 0;
+    for x in 0..data.width {
+        for y in 0..data.height {
+            if data[Point::new(x, y)] == b'X' {
+                result += if validate(x, y, 1, 0) { 1 } else { 0 };
+                result += if validate(x, y, -1, 0) { 1 } else { 0 };
+                result += if validate(x, y, 0, 1) { 1 } else { 0 };
+                result += if validate(x, y, 0, -1) { 1 } else { 0 };
+
+                result += if validate(x, y, 1, 1) { 1 } else { 0 };
+                result += if validate(x, y, 1, -1) { 1 } else { 0 };
+                result += if validate(x, y, -1, 1) { 1 } else { 0 };
+                result += if validate(x, y, -1, -1) { 1 } else { 0 };
+            }
+        }
+    }
+
+    Some(result)
+}
+
+pub fn part_two(input: &str) -> Option<u32> {
+    let data = parse_data(input);
+
+    const MAS_LIST: [[u8; 4]; 4] = [
+        [b'M', b'M', b'S', b'S'],
+        [b'M', b'S', b'M', b'S'],
+        [b'S', b'S', b'M', b'M'],
+        [b'S', b'M', b'S', b'M'],
+    ];
+
+    let mut result = 0;
+    for x in 1..data.width - 1 {
+        for y in 1..data.height - 1 {
+            if data[Point::new(x, y)] == b'A' {
+                let a = [
+                    data[Point::new(x - 1, y + 1)],
+                    data[Point::new(x + 1, y + 1)],
+                    data[Point::new(x - 1, y - 1)],
+                    data[Point::new(x + 1, y - 1)],
+                ];
+
+                if MAS_LIST.contains(&a) {
+                    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));
+    }
+}