From ca4a125deb84700b08e6e7aeb5b882fd14d85c6d Mon Sep 17 00:00:00 2001
From: Reiner Herrmann <reiner@reiner-h.de>
Date: Sat, 11 Dec 2021 14:11:24 +0100
Subject: day11

---
 src/bin/day11.rs | 144 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 144 insertions(+)
 create mode 100644 src/bin/day11.rs

(limited to 'src/bin/day11.rs')

diff --git a/src/bin/day11.rs b/src/bin/day11.rs
new file mode 100644
index 0000000..d5879bb
--- /dev/null
+++ b/src/bin/day11.rs
@@ -0,0 +1,144 @@
+use std::collections::HashMap;
+
+fn main() {
+    let input = advent::read_lines(11);
+    println!("11a: {}", count_flashes(&input, 100));
+    println!("11b: {}", all_flashing(&input));
+}
+
+#[derive(PartialEq,Eq,Hash,Copy,Clone)]
+struct Position {
+    x: isize,
+    y: isize,
+}
+
+#[derive(Clone)]
+struct OctopusCavern {
+    grid: HashMap<Position,i8>,
+    flashes: usize,
+}
+
+impl OctopusCavern {
+    fn new<T: AsRef<str>>(input: &[T]) -> OctopusCavern {
+        let mut grid = HashMap::new();
+        for (y, line) in input.iter().enumerate() {
+            for (x, c) in line.as_ref().split_terminator("").skip(1).enumerate() {
+                let level = c.parse::<i8>().unwrap();
+                grid.insert(Position { x: x as isize, y: y as isize }, level);
+            }
+        }
+        OctopusCavern { grid, flashes: 0 }
+    }
+
+    fn increment_levels(&mut self) {
+        for (_, level) in self.grid.iter_mut() {
+            *level += 1;
+        }
+    }
+
+    fn can_flash(&self) -> bool {
+        self.grid.values().any(|&level| level > 9)
+    }
+
+    fn flash(&mut self) {
+        let mut new_grid = self.grid.clone();
+
+        for pos in self.grid.iter().filter(|(_,&level)| level > 9).map(|(&pos,_)| pos) {
+            self.flashes += 1;
+            new_grid.insert(pos, -1);
+            for x in -1 ..= 1 {
+                for y in -1 ..= 1 {
+                    if (x, y) == (0, 0) {
+                        continue
+                    }
+
+                    if let Some(level) = new_grid.get_mut(&Position { x: pos.x + x, y: pos.y + y }) {
+                        if *level != -1 {
+                            *level += 1;
+                        }
+                    }
+                }
+            }
+        }
+
+        self.grid = new_grid;
+    }
+
+    fn reset_levels(&mut self) {
+        for level in self.grid.values_mut() {
+            if *level == -1 {
+                *level = 0;
+            }
+        }
+    }
+
+    fn step(&mut self) {
+        assert!(!self.can_flash());
+        self.increment_levels();
+        while self.can_flash() {
+            self.flash();
+        }
+        self.reset_levels();
+    }
+
+    fn all_flashing(&self) -> bool {
+        !self.grid.values().any(|&level| level > 0)
+    }
+}
+
+
+fn count_flashes<T: AsRef<str>>(input: &[T], steps: usize) -> usize {
+    let mut cavern = OctopusCavern::new(input);
+    for _ in 0 .. steps {
+        cavern.step();
+    }
+    cavern.flashes
+}
+
+fn all_flashing<T: AsRef<str>>(input: &[T]) -> usize {
+    let mut cavern = OctopusCavern::new(input);
+    let mut step = 0;
+    loop {
+        step += 1;
+        cavern.step();
+        if cavern.all_flashing() {
+            return step;
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test0() {
+        let input = [
+            "11111",
+            "19991",
+            "19191",
+            "19991",
+            "11111",
+        ];
+        assert_eq!(count_flashes(&input, 2), 9);
+    }
+
+    #[test]
+    fn test1() {
+        let input = [
+            "5483143223",
+            "2745854711",
+            "5264556173",
+            "6141336146",
+            "6357385478",
+            "4167524645",
+            "2176841721",
+            "6882881134",
+            "4846848554",
+            "5283751526",
+        ];
+        assert_eq!(count_flashes(&input, 100), 1656);
+        assert_eq!(all_flashing(&input), 195);
+    }
+
+}
-- 
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