diff --git a/day-11/Cargo.lock b/day-11/Cargo.lock
new file mode 100644
index 0000000..5e329eb
--- /dev/null
+++ b/day-11/Cargo.lock
@@ -0,0 +1,78 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+[[package]]
+name = "day-11"
+version = "0.1.0"
+dependencies = [
+ "indoc",
+]
+
+[[package]]
+name = "indoc"
+version = "0.3.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "47741a8bc60fb26eb8d6e0238bbb26d8575ff623fdc97b1a2c00c050b9684ed8"
+dependencies = [
+ "indoc-impl",
+ "proc-macro-hack",
+]
+
+[[package]]
+name = "indoc-impl"
+version = "0.3.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ce046d161f000fffde5f432a0d034d0341dc152643b2598ed5bfce44c4f3a8f0"
+dependencies = [
+ "proc-macro-hack",
+ "proc-macro2",
+ "quote",
+ "syn",
+ "unindent",
+]
+
+[[package]]
+name = "proc-macro-hack"
+version = "0.5.19"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "dbf0c48bc1d91375ae5c3cd81e3722dff1abcf81a30960240640d223f59fe0e5"
+
+[[package]]
+name = "proc-macro2"
+version = "1.0.24"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1e0704ee1a7e00d7bb417d0770ea303c1bccbabf0ef1667dae92b5967f5f8a71"
+dependencies = [
+ "unicode-xid",
+]
+
+[[package]]
+name = "quote"
+version = "1.0.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "aa563d17ecb180e500da1cfd2b028310ac758de548efdd203e18f283af693f37"
+dependencies = [
+ "proc-macro2",
+]
+
+[[package]]
+name = "syn"
+version = "1.0.54"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9a2af957a63d6bd42255c359c93d9bfdb97076bd3b820897ce55ffbfbf107f44"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "unicode-xid",
+]
+
+[[package]]
+name = "unicode-xid"
+version = "0.2.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f7fe0bb3479651439c9112f72b6c505038574c9fbb575ed1bf3b797fa39dd564"
+
+[[package]]
+name = "unindent"
+version = "0.1.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f14ee04d9415b52b3aeab06258a3f07093182b88ba0f9b8d203f211a7a7d41c7"
diff --git a/day-11/Cargo.toml b/day-11/Cargo.toml
new file mode 100644
index 0000000..5cf3b01
--- /dev/null
+++ b/day-11/Cargo.toml
@@ -0,0 +1,10 @@
+[package]
+name = "day-11"
+version = "0.1.0"
+authors = ["Tristan Daniël Maat <tm@tlater.net>"]
+edition = "2018"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+indoc = "0.3"
diff --git a/day-11/input b/day-11/input
new file mode 100644
index 0000000..7cf41d9
--- /dev/null
+++ b/day-11/input
@@ -0,0 +1,93 @@
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diff --git a/day-11/src/main.rs b/day-11/src/main.rs
new file mode 100644
index 0000000..886261d
--- /dev/null
+++ b/day-11/src/main.rs
@@ -0,0 +1,180 @@
+use std::fs;
+
+fn main() -> Result<(), Box<dyn std::error::Error>> {
+ let input = fs::read_to_string("input")?;
+ let layout = parse_layout(&input)?;
+
+ // Part 1
+ let result = count_eventually_occupied_seats(&layout);
+ println!("{}", result);
+
+ Ok(())
+}
+
+#[derive(Copy, Clone, Debug, PartialEq)]
+enum Seating {
+ Occupied,
+ Empty,
+ Floor,
+}
+
+impl Seating {
+ fn new(symbol: char) -> Result<Self, String> {
+ match symbol {
+ '#' => Ok(Seating::Occupied),
+ 'L' => Ok(Seating::Empty),
+ '.' => Ok(Seating::Floor),
+ rubbish => Err(format!("Found some rubbish on the floor, area must be clean to conserve human behavior: {}", rubbish))
+ }
+ }
+}
+
+fn parse_layout(input: &str) -> Result<Vec<Vec<Seating>>, String> {
+ input
+ .lines()
+ .map(|line| line.chars().map(Seating::new).collect())
+ .collect()
+}
+
+fn print_layout(layout: &Vec<Vec<Seating>>) {
+ let output: String = layout
+ .iter()
+ .map(|row| {
+ let mut row: String = row
+ .iter()
+ .map(|c| match c {
+ Seating::Occupied => '#',
+ Seating::Empty => 'L',
+ Seating::Floor => '.',
+ })
+ .collect();
+ row.push('\n');
+ row
+ })
+ .collect();
+
+ println!("{}", output);
+}
+
+fn get_adjacent(layout: &Vec<Vec<Seating>>, i: usize, j: usize) -> Vec<Option<&Seating>> {
+ let adjacent: [[usize; 2]; 8] = [
+ [0, 0],
+ [0, 1],
+ [0, 2],
+ [1, 0],
+ [1, 2],
+ [2, 0],
+ [2, 1],
+ [2, 2],
+ ];
+
+ adjacent
+ .iter()
+ .map(|[nudge_row, nudge_col]| {
+ if let Some(row) = (i + nudge_row).checked_sub(1) {
+ if let Some(row) = layout.get(row) {
+ if let Some(col) = (j + nudge_col).checked_sub(1) {
+ row.get(col)
+ } else {
+ None
+ }
+ } else {
+ None
+ }
+ } else {
+ None
+ }
+ })
+ .collect()
+}
+
+fn simulate_people(layout: &Vec<Vec<Seating>>) -> (Vec<Vec<Seating>>, usize) {
+ let mut changes = 0;
+
+ let layout = layout
+ .iter()
+ .enumerate()
+ .map(|(i, row)| {
+ row.iter()
+ .enumerate()
+ .map(|(j, seat)| match seat {
+ Seating::Occupied => {
+ if get_adjacent(layout, i, j)
+ .iter()
+ .filter(|seat| **seat == Some(&Seating::Occupied))
+ .count()
+ >= 4
+ {
+ changes += 1;
+ Seating::Empty
+ } else {
+ Seating::Occupied
+ }
+ }
+ Seating::Empty => {
+ if get_adjacent(layout, i, j)
+ .iter()
+ .any(|seat| *seat == Some(&Seating::Occupied))
+ {
+ Seating::Empty
+ } else {
+ changes += 1;
+ Seating::Occupied
+ }
+ }
+ Seating::Floor => Seating::Floor,
+ })
+ .collect()
+ })
+ .collect();
+
+ (layout, changes)
+}
+
+fn count_eventually_occupied_seats(layout: &Vec<Vec<Seating>>) -> usize {
+ let mut loop_layout = layout.clone();
+
+ loop {
+ let (res, changes) = simulate_people(&loop_layout);
+ loop_layout = res;
+
+ if changes == 0 {
+ break;
+ }
+ }
+
+ loop_layout
+ .iter()
+ .flatten()
+ .filter(|seat| **seat == Seating::Occupied)
+ .count()
+}
+
+#[cfg(test)]
+mod tests {
+ use super::*;
+ use indoc::indoc;
+
+ #[test]
+ fn test_simple() -> Result<(), Box<dyn std::error::Error>> {
+ let input = indoc!(
+ "L.LL.LL.LL
+ LLLLLLL.LL
+ L.L.L..L..
+ LLLL.LL.LL
+ L.LL.LL.LL
+ L.LLLLL.LL
+ ..L.L.....
+ LLLLLLLLLL
+ L.LLLLLL.L
+ L.LLLLL.LL
+ "
+ );
+
+ let layout = parse_layout(&input)?;
+ let result = count_eventually_occupied_seats(&layout);
+
+ assert_eq!(result, 37);
+ Ok(())
+ }
+}