1 files changed, 82 insertions, 0 deletions
diff --git a/2023/day21.rs b/2023/day21.rs
new file mode 100644
index 0000000..c533177
--- /dev/null
+++ b/2023/day21.rs
@@ -0,0 +1,82 @@
+#![allow(dead_code)]
+#![allow(unused_variables)]
+#![allow(unused_mut)]
+use std::collections::HashSet;
+use std::env;
+use std::fs::File;
+use std::io::Read;
+
+// #[derive(Hash, Eq, Debug, PartialEq, Clone, Copy)]
+// enum Field {
+//     Empty,
+//     Rock,
+//     Start,
+// }
+
+type Matrix<T> = Vec<Vec<T>>;
+
+fn bfs(steps: usize, x0: usize, y0: usize, m: &Matrix<bool>) -> usize {
+    let mut hs: HashSet<(usize, usize)> = HashSet::new();
+    let mut hs_next: HashSet<(usize, usize)> = HashSet::new();
+    hs.insert((x0, y0));
+
+    for s in 0..steps {
+        for (x, y) in hs {
+            if x + 1 < m[0].len() && m[y][x + 1] {
+                hs_next.insert((x + 1, y));
+            }
+            if x as i32 - 1 >= 0 && m[y][x - 1] {
+                hs_next.insert((x - 1, y));
+            }
+            if y + 1 < m.len() && m[y + 1][x] {
+                hs_next.insert((x, y + 1));
+            }
+            if y as i32 - 1 >= 0 && m[y - 1][x] {
+                hs_next.insert((x, y - 1));
+            }
+        }
+        hs = hs_next;
+        hs_next = HashSet::new();
+    }
+    return hs.len();
+}
+
+fn main() {
+    let args: Vec<String> = env::args().collect();
+    let filename = if args.len() == 1 {
+        "in/".to_owned() + args[0].split('/').last().unwrap() + ".pzl"
+    } else {
+        args[1].clone()
+    };
+    let mut f = File::open(filename).expect("cannot open file");
+    let mut content = String::new();
+    f.read_to_string(&mut content).expect("cannot read file");
+    let lines = content.trim_end().split("\n");
+
+    let mut x0: usize = 0;
+    let mut y0: usize = 0;
+    let mut m: Matrix<bool> = Vec::new();
+    for (y, line) in lines.enumerate() {
+        let mut r: Vec<bool> = Vec::new();
+        for (x, c) in line.chars().enumerate() {
+            match c {
+                '.' => r.push(true),
+                '#' => r.push(false),
+                'S' => {
+                    r.push(true);
+                    x0 = x;
+                    y0 = y;
+                }
+                _ => panic!(),
+            };
+        }
+        m.push(r);
+    }
+
+    let res1 = bfs(64, x0, y0, &m);
+
+    let mut res2 = 0;
+
+    println!("res1: {}", res1);
+    println!("res2: {}", res2);
+}