1 files changed, 116 insertions, 0 deletions
diff --git a/11/src/main.rs b/11/src/main.rs
new file mode 100644
index 0000000..566176c
--- /dev/null
+++ b/11/src/main.rs
@@ -0,0 +1,116 @@
+use advent_lib::prelude::*;
+
+
+fn main() -> Result<()> {
+  let mut args = std::env::args();
+  if args.len() != 2 {
+    eprintln!("Usage: advent input");
+  }
+  let _ = args.next();
+  let filename = args.next().unwrap();
+
+  let input = advent_lib::read_lines_file(&filename)?;
+
+  let mut grid = Vec::new();
+  for line in &input {
+    let mut row = Vec::new();
+    for c in line.chars() {
+      let value: i64 = c.to_digit(10).unwrap() as i64;
+      row.push(value);
+    }
+    grid.push(row);
+  }
+
+  let mut n_flashes = 0;
+  for _ in 0 .. 100 {
+    n_flashes += iterate(&mut grid);
+  }
+  println!("{}", n_flashes);
+
+  for i in 101 .. 1000000 {
+    if iterate(&mut grid) == 100 {
+      println!("{}", i);
+      break;
+    }
+  }
+
+  Ok(())
+}
+
+
+#[allow(dead_code)]
+fn debug_grid(grid: &Vec<Vec<i64>>) {
+  for row in grid {
+    for cell in row {
+      print!(" {}", cell)
+    }
+    println!("");
+  }
+  println!("");
+}
+
+
+
+fn iterate(grid: &mut Vec<Vec<i64>>) -> i64 {
+  let height = grid.len();
+  let width = grid[0].len();
+
+  let mut has_flashed = Vec::new();
+  for _ in 0 .. height {
+    let mut has_flashed_row = Vec::new();
+    for _ in 0 .. width {
+      has_flashed_row.push(false);
+    }
+    has_flashed.push(has_flashed_row);
+  }
+
+  for y in 0 .. height {
+    for x in 0 .. width {
+      grid[y][x] += 1;
+    }
+  }
+
+  let mut n_flashes = 0;
+  loop {
+    let mut any_flashes = false;
+
+    for y in 0 .. height {
+      for x in 0 .. width {
+        if (grid[y][x] > 9) && !has_flashed[y][x] {
+          n_flashes += 1;
+          has_flashed[y][x] = true;
+          any_flashes = true;
+
+          for (dx, dy) in &[(-1, -1), (0, -1), (1, -1),
+                            (-1, 0),           (1, 0),
+                            (-1, 1),  (0, 1),  (1, 1)]
+          {
+            let adjacent_x = x as i64 + dx;
+            let adjacent_y = y as i64 + dy;
+
+            if (adjacent_x >= 0) && (adjacent_x < width as i64)
+              && (adjacent_y >= 0) && (adjacent_y < height as i64)
+            {
+              grid[adjacent_y as usize][adjacent_x as usize] += 1;
+            }
+          }
+        }
+      }
+    }
+
+    if !any_flashes {
+      break;
+    }
+  }
+
+  for y in 0 .. height {
+    for x in 0 .. width {
+      if has_flashed[y][x] {
+        grid[y][x] = 0;
+      }
+    }
+  }
+
+  n_flashes
+}
+