1 files changed, 130 insertions, 0 deletions
diff --git a/2021/src/bin/day_11.rs b/2021/src/bin/day_11.rs
new file mode 100644
index 0000000..2a4cd89
--- /dev/null
+++ b/2021/src/bin/day_11.rs
@@ -0,0 +1,130 @@
+use nom::{
+    character::complete::{line_ending, one_of},
+    combinator::map_res,
+    multi::{many1, separated_list1},
+    IResult,
+};
+use std::fs;
+
+fn main() -> Result<(), Box<dyn std::error::Error>> {
+    let input = fs::read_to_string("inputs/day_11.txt")?;
+    let squid_grid = parse_squid_grid(&input).unwrap().1;
+
+    {
+        let mut squid_grid = squid_grid.clone();
+        let mut flashes_on_100 = 0;
+        for _ in 0..100 {
+            flashes_on_100 += squid_grid.flash();
+        }
+        dbg!(flashes_on_100);
+    }
+
+    {
+        let mut squid_grid = squid_grid.clone();
+        let sync_time = std::iter::repeat_with(|| squid_grid.flash())
+            .position(|flashes| flashes == 100)
+            .map(|x| x + 1);
+        dbg!(sync_time);
+    }
+
+    Ok(())
+}
+
+#[derive(Debug, Clone)]
+struct Squid {
+    energy: u8,
+    has_flashed: bool,
+}
+
+impl Squid {
+    fn should_flash(&self) -> bool {
+        self.energy > 9 && !self.has_flashed
+    }
+
+    fn reset(&mut self) {
+        self.energy = 0;
+        self.has_flashed = false;
+    }
+}
+
+#[derive(Debug, Clone)]
+struct SquidGrid {
+    squids: [[Squid; 10]; 10],
+}
+
+impl SquidGrid {
+    fn flash(&mut self) -> usize {
+        for y in 0..10 {
+            for x in 0..10 {
+                self.squids[y][x].energy += 1;
+            }
+        }
+
+        let mut any_new_flashes = true;
+        while any_new_flashes {
+            any_new_flashes = false;
+            for y in 0..10 {
+                for x in 0..10 {
+                    if self.squids[y][x].should_flash() {
+                        any_new_flashes = true;
+                        self.squids[y][x].has_flashed = true;
+                        if y > 0 && x > 0 {
+                            self.squids[y - 1][x - 1].energy += 1;
+                        }
+                        if y > 0 {
+                            self.squids[y - 1][x].energy += 1;
+                        }
+                        if y > 0 && x < 9 {
+                            self.squids[y - 1][x + 1].energy += 1;
+                        }
+                        if x > 0 {
+                            self.squids[y][x - 1].energy += 1;
+                        }
+                        if x < 9 {
+                            self.squids[y][x + 1].energy += 1;
+                        }
+                        if y < 9 && x > 0 {
+                            self.squids[y + 1][x - 1].energy += 1;
+                        }
+                        if y < 9 {
+                            self.squids[y + 1][x].energy += 1;
+                        }
+                        if y < 9 && x < 9 {
+                            self.squids[y + 1][x + 1].energy += 1;
+                        }
+                    }
+                }
+            }
+        }
+
+        let mut flashes = 0;
+        for y in 0..10 {
+            for x in 0..10 {
+                if self.squids[y][x].has_flashed {
+                    self.squids[y][x].reset();
+                    flashes += 1;
+                }
+            }
+        }
+        flashes
+    }
+}
+
+fn parse_squid_grid(input: &str) -> IResult<&str, SquidGrid> {
+    map_res(separated_list1(line_ending, parse_squid_row), |squids| {
+        squids.try_into().map(|squids| SquidGrid { squids })
+    })(input)
+}
+
+fn parse_squid_row(input: &str) -> IResult<&str, [Squid; 10]> {
+    map_res(many1(parse_squid), |squids| squids.try_into())(input)
+}
+
+fn parse_squid(input: &str) -> IResult<&str, Squid> {
+    map_res(one_of("0123456789"), |digit| {
+        digit.to_string().parse().map(|energy| Squid {
+            energy,
+            has_flashed: false,
+        })
+    })(input)
+}