Day 4 done

2024/rust/src/day4.rs

@@ -0,0 +1,148 @@
+mod prelude;
+pub use crate::prelude::*;
+
+fn main() {
+    let input = day_input(4);
+    show_answers(count_xmas(&input), count_mas_x(&input));
+}
+
+fn count_xmas(input: &str) -> usize {
+    let grid: Vec<Vec<u8>> = input
+        .trim()
+        .lines()
+        .map(|l| l.trim().bytes().collect())
+        .collect();
+    println!("{grid:?}\n{input}");
+    let height = grid.len();
+    let width = grid[0].len();
+    let mut counter = 0;
+
+    const XMAS: (u8, u8, u8, u8) = (b'X', b'M', b'A', b'S');
+    const SAMX: (u8, u8, u8, u8) = (b'S', b'A', b'M', b'X');
+
+    for (y, line) in grid.iter().enumerate() {
+        for (x, letter) in line.iter().enumerate() {
+            // let near_left_edge = x < 3;
+            let near_top_edge = y < 3;
+            let near_right_edge = x >= width - 3;
+            let near_bottom_edge = y >= height - 3;
+
+            // println!("{x} {y} {width} {height} {near_right_edge} {near_top_edge}");
+
+            if !near_right_edge && !near_top_edge {
+                // north-west
+                let ray = (
+                    *letter,
+                    grid[y - 1][x + 1],
+                    grid[y - 2][x + 2],
+                    grid[y - 3][x + 3],
+                );
+                if ray == XMAS || ray == SAMX {
+                    counter += 1;
+                    println!("north-west @ {x} {y} {counter}");
+                }
+            }
+
+            if !near_right_edge {
+                // west
+                let ray = (*letter, grid[y][x + 1], grid[y][x + 2], grid[y][x + 3]);
+                if ray == XMAS || ray == SAMX {
+                    counter += 1;
+                    println!("west @ {x} {y} {counter}");
+                }
+            }
+
+            if !near_right_edge && !near_bottom_edge {
+                // south-west
+                let ray = (
+                    *letter,
+                    grid[y + 1][x + 1],
+                    grid[y + 2][x + 2],
+                    grid[y + 3][x + 3],
+                );
+                if ray == XMAS || ray == SAMX {
+                    counter += 1;
+                    println!("south-west @ {x} {y} {counter}");
+                }
+            }
+
+            if !near_bottom_edge {
+                // south
+                let ray = (*letter, grid[y + 1][x], grid[y + 2][x], grid[y + 3][x]);
+                if ray == XMAS || ray == SAMX {
+                    counter += 1;
+                    println!("south @ {x} {y} {counter}");
+                }
+            }
+        }
+    }
+    counter
+}
+
+fn count_mas_x(input: &str) -> usize {
+    let grid: Vec<Vec<u8>> = input
+        .trim()
+        .lines()
+        .map(|l| l.trim().bytes().collect())
+        .collect();
+    println!("{grid:?}\n{input}");
+    let height = grid.len();
+    let width = grid[0].len();
+    let mut counter = 0;
+    for y in 1..height - 1 {
+        for x in 1..width - 1 {
+            println!("{x} {y} {}", grid[y][x]);
+            if grid[y][x] != b'A' {
+                continue;
+            }
+            let ray1 = (grid[y - 1][x - 1], grid[y + 1][x + 1]);
+            let ray2 = (grid[y + 1][x - 1], grid[y - 1][x + 1]);
+            println!("{x} {y} {ray1:?} {ray2:?} (S: {:?}, M: {:?})", b'S', b'M');
+            if (ray1 == (b'M', b'S') || ray1 == (b'S', b'M'))
+                && (ray2 == (b'M', b'S') || ray2 == (b'S', b'M'))
+            {
+                counter += 1;
+            }
+        }
+    }
+    counter
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test() {
+        assert_eq!(
+            count_xmas(
+                r#"MMMSXXMASM
+MSAMXMSMSA
+AMXSXMAAMM
+MSAMASMSMX
+XMASAMXAMM
+XXAMMXXAMA
+SMSMSASXSS
+SAXAMASAAA
+MAMMMXMMMM
+MXMXAXMASX"#
+            ),
+            18
+        );
+        assert_eq!(
+            count_mas_x(
+                r#"MMMSXXMASM
+MSAMXMSMSA
+AMXSXMAAMM
+MSAMASMSMX
+XMASAMXAMM
+XXAMMXXAMA
+SMSMSASXSS
+SAXAMASAAA
+MAMMMXMMMM
+MXMXAXMASX"#
+            ),
+            9
+        );
+    }
+}