diff --git a/2016/rust/src/day_02.rs b/2016/rust/src/day_02.rs
new file mode 100644
index 0000000..8073eec
--- /dev/null
+++ b/2016/rust/src/day_02.rs
@@ -0,0 +1,95 @@
+use std::char;
+
+pub fn solve(input: &str) -> String {
+ let arrangement = vec![
+ vec!['1', '2', '3'],
+ vec!['4', '5', '6'],
+ vec!['7', '8', '9'],
+ ];
+ let mut keypad = Keypad {
+ arrangement: arrangement,
+ current: (1, 1),
+ };
+
+ let mut answer = String::new();
+ for c in input.chars() {
+ match c {
+ 'U' => { keypad.move_(Dir::Up); },
+ 'D' => { keypad.move_(Dir::Down); },
+ 'L' => { keypad.move_(Dir::Left); },
+ 'R' => { keypad.move_(Dir::Right); },
+ '\n' => { answer.push(keypad.button()); },
+ _ => { unreachable!(); },
+ }
+ }
+ answer.push(keypad.button());
+ answer
+}
+
+#[test]
+fn test_solve() {
+ let instructions = "ULL
+RRDDD
+LURDL
+UUUUD";
+
+ assert_eq!(solve(instructions), "1985".to_string());
+}
+
+struct Keypad {
+ arrangement: Vec<Vec<char>>,
+ current: (usize, usize),
+}
+
+impl Keypad {
+ fn move_(&mut self, dir: Dir) {
+ let (dx, dy): (isize, isize) = match dir {
+ Dir::Up => (0, -1),
+ Dir::Down => (0, 1),
+ Dir::Left => (-1, 0),
+ Dir::Right => (1, 0),
+ };
+
+ let x = (self.current.0 as isize + dx) as usize;
+ let y = (self.current.1 as isize + dy) as usize;
+
+ if self.button_at(x, y).is_some() {
+ self.current = (x, y);
+ }
+ }
+
+ fn button(&self) -> char {
+ let (x, y) = self.current;
+ self.arrangement[y][x].clone()
+ }
+
+ fn button_at(&self, x: usize, y: usize) -> Option<char> {
+ self.arrangement.get(y).and_then(|row| row.get(x)).cloned()
+ }
+}
+
+enum Dir {
+ Up, Down, Left, Right
+}
+
+#[test]
+fn test_keypad() {
+ let arrangement = vec![
+ vec!['1', '2', '3'],
+ vec!['4', '5', '6'],
+ vec!['7', '8', '9'],
+ ];
+ let mut keypad = Keypad {
+ arrangement: arrangement,
+ current: (1, 1),
+ };
+
+ assert_eq!(keypad.button_at(1, 1), Some('5'));
+ assert_eq!(keypad.button(), '5');
+
+ keypad.move_(Dir::Up);
+ assert_eq!(keypad.button(), '2');
+
+ keypad.move_(Dir::Up);
+ assert_eq!(keypad.button(), '2');
+}
diff --git a/2016/rust/src/lib.rs b/2016/rust/src/lib.rs
index 83a7f75..f396c42 100644
--- a/2016/rust/src/lib.rs
+++ b/2016/rust/src/lib.rs
@@ -1 +1,2 @@
pub mod day_01;
+pub mod day_02;
diff --git a/2016/rust/src/main.rs b/2016/rust/src/main.rs
index 3742d65..bbd3b10 100644
--- a/2016/rust/src/main.rs
+++ b/2016/rust/src/main.rs
@@ -8,5 +8,5 @@ fn main() {
let mut input = String::new();
io::stdin().read_to_string(&mut input).ok();
- println!("{}", day_01::solve(&input));
+ println!("{}", day_02::solve(&input));
}