Add solution for 2024 day 4 part 2

2024/day-04/part_two.rs

@@ -0,0 +1,80 @@
+use std::path::Path;
+use std::{env, fs};
+
+
+fn main() {
+    let input_file = env::args().nth(1).expect("requires input file");
+
+    let input = PuzzleInput::parse(input_file);
+
+    let num_xmas = count_xmas(&input);
+
+    println!("{num_xmas}");
+}
+
+
+fn count_xmas(input: &PuzzleInput) -> usize {
+    let mut count = 0;
+
+    for (row_off, row) in input.map.iter().enumerate() {
+        for (cell_off, cell) in row.iter().enumerate() {
+            if *cell == 'A' {
+                if find_x(input, row_off, cell_off) {
+                    count += 1;
+                }
+            }
+        }
+    }
+
+    count
+}
+
+
+fn find_x(input: &PuzzleInput, row_off: usize, cell_off: usize) -> bool {
+    let map = &input.map;
+    let (right, bottom) = (map[0].len() as isize, map.len() as isize);
+
+    for offset in [0, 2] {
+        let x1 = (cell_off as isize + 1) - offset;
+        let x2 = (cell_off as isize - 1) + offset;
+
+        let y1 = (row_off as isize) + 1;
+        let y2 = (row_off as isize) + -1;
+
+        if x1 < 0 || x1 >= right || x2 < 0 || x2 >= right {
+            return false;
+        }
+
+        if y1 < 0 || y1 >= bottom || y2 < 0 || y2 >= bottom {
+            return false;
+        }
+
+        let side_a = map[y1 as usize][x1 as usize];
+        let side_b = map[y2 as usize][x2 as usize];
+
+        if !(side_a == 'M' && side_b == 'S' || side_a == 'S' && side_b == 'M') {
+            return false;
+        }
+    }
+
+    true
+}
+
+
+#[derive(Debug)]
+pub struct PuzzleInput {
+    map: Vec<Vec<char>>,
+}
+
+impl PuzzleInput {
+    pub fn parse<P>(path: P) -> Self
+    where
+        P: AsRef<Path>,
+    {
+        let content = fs::read_to_string(path).unwrap();
+
+        let map = content.lines().map(|line| line.chars().collect()).collect();
+
+        Self { map }
+    }
+}