diff --git a/day23/Cargo.toml b/day23/Cargo.toml
new file mode 100644
index 0000000..0468a8b
--- /dev/null
+++ b/day23/Cargo.toml
@@ -0,0 +1,9 @@
+[package]
+name = "day23"
+version = "0.1.0"
+authors = ["inga-lovinde <52715130+inga-lovinde@users.noreply.github.com>"]
+edition = "2018"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
diff --git a/day23/src/main.rs b/day23/src/main.rs
new file mode 100644
index 0000000..0ce7d66
--- /dev/null
+++ b/day23/src/main.rs
@@ -0,0 +1,168 @@
+use std::fmt;
+use std::{io::{self, BufRead}};
+
+#[derive(Clone, Copy)]
+struct Entry {
+    previous_value: usize,
+    next_value: usize,
+}
+
+struct GameState {
+    current_cup: usize,
+    state: Vec<Entry>,
+}
+
+impl GameState {
+    fn new(raw_data: &[usize]) -> GameState {
+        let data: Vec<_> = raw_data.iter().map(|&x| x-1).collect();
+        let mut state = vec![None; data.len()];
+        state[data[0]] = Some(Entry {
+            previous_value: data[data.len()-1],
+            next_value: data[1],
+        });
+        for i in 1..data.len()-1 {
+            state[data[i]] = Some(Entry {
+                previous_value: data[i-1],
+                next_value: data[i+1],
+            });
+        }
+        state[data[data.len()-1]] = Some(Entry {
+            previous_value: data[data.len()-2],
+            next_value: data[0],
+        });
+
+        GameState {
+            current_cup: data[0],
+            state: state.into_iter().collect::<Option<_>>().unwrap(),
+        }
+    }
+
+    fn get_next_value(&self, value: usize) -> usize {
+        self.state[value].next_value
+    }
+
+    // unsafe, leaves self in an inconsistent state, only invoke from link_values
+    fn set_next_value(&mut self, value: usize, new_next_value: usize) {
+        self.state[value] = Entry {
+            next_value: new_next_value,
+            ..self.state[value]
+        }
+    }
+
+    // unsafe, leaves self in an inconsistent state, only invoke from link_values
+    fn set_previous_value(&mut self, value: usize, new_previous_value: usize) {
+        self.state[value] = Entry {
+            previous_value: new_previous_value,
+            ..self.state[value]
+        }
+    }
+
+    // unsafe, leaves self in an inconsistent state, only invoke from move_value
+    fn link_values(&mut self, previous_value: usize, next_value: usize) {
+        self.set_next_value(previous_value, next_value);
+        self.set_previous_value(next_value, previous_value);
+    }
+
+    fn move_value(&mut self, value: usize, new_previous: usize) {
+        let old_previous = self.state[value].previous_value;
+        let old_next = self.state[value].next_value;
+        let new_next = self.state[new_previous].next_value;
+        self.link_values(old_previous, old_next);
+        self.link_values(new_previous, value);
+        self.link_values(value, new_next);
+    }
+
+    fn get_destination_cup(&self, current_cup: usize) -> usize {
+        let blacklisted_cups = [
+            current_cup,
+            self.get_next_value(current_cup),
+            self.get_next_value(self.get_next_value(current_cup)),
+            self.get_next_value(self.get_next_value(self.get_next_value(current_cup))),
+        ];
+
+        let mut destination_label = current_cup;
+        loop {
+            if destination_label == 0 {
+                destination_label = self.state.len();
+            }
+            destination_label -= 1;
+
+            if !blacklisted_cups.contains(&destination_label) {
+                return destination_label;
+            }
+        }
+    }
+
+    fn mutate_next_step(&mut self) {
+        let current_cup = self.current_cup;
+        let mut destination_cup = self.get_destination_cup(current_cup);
+        for _i in 0..3 {
+            let value_to_move = self.get_next_value(current_cup);
+            self.move_value(value_to_move, destination_cup);
+            destination_cup = value_to_move;
+        }
+        
+        self.current_cup = self.get_next_value(current_cup);
+    }
+
+    fn get_hard_result(&self) -> u64 {
+        (self.get_next_value(0) as u64 + 1) * (self.get_next_value(self.get_next_value(0)) as u64 + 1)
+    }
+}
+
+impl fmt::Debug for GameState {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let mut list = Vec::with_capacity(self.state.len());
+        list.push(1);
+        let mut current_value = self.get_next_value(0);
+        while current_value != 0 {
+            list.push(current_value + 1);
+            current_value = self.get_next_value(current_value);
+        }
+
+        f.debug_struct("GameState")
+            .field("current_cup", &(self.current_cup + 1))
+            .field("cups", &list)
+            .finish()
+    }
+}
+
+fn game_simple(original_data: &[usize]) {
+    let mut state = GameState::new(&original_data);
+
+    for i in 0..=100 {
+        println!("{}: {:?}", i, state);
+        state.mutate_next_step();
+    }
+}
+
+fn game_hard(original_data: &[usize]) {
+    let mut state = GameState::new(&original_data);
+
+    for i in 0..10_000_000 {
+        if i % 10_000 == 0 {
+            println!("Step {}", i);
+        }
+        state.mutate_next_step();
+    }
+
+    println!("{}", state.get_hard_result());
+}
+
+fn main() {
+    let stdin = io::stdin();
+    let mut lines = stdin.lock().lines();
+    let line = lines.next().unwrap().unwrap();
+    let original_state: Vec<usize> = line.chars().map(|ch| ch.to_string().parse().unwrap()).collect();
+    game_simple(&original_state);
+
+    let mut hard_state = Vec::with_capacity(1_000_000);
+    for i in 0..original_state.len() {
+        hard_state.push(original_state[i]);
+    }
+
+    for i in original_state.len()..1_000_000 {
+        hard_state.push(i+1);
+    }
+    game_hard(&hard_state);
+}