Add day 9

Cargo.toml

@@ -41,4 +41,8 @@ path = "src/day7/main.rs"
 name = "day8"
 path = "src/day8/main.rs"
 
+[[bin]]
+name = "day9"
+path = "src/day9/main.rs"
+
 [dependencies]

day9_test.txt

@@ -0,0 +1,8 @@
+R 4
+U 4
+L 3
+D 1
+R 4
+D 1
+L 5
+R 2

day9_test_2.txt

@@ -0,0 +1,8 @@
+R 5
+U 8
+L 8
+D 3
+R 17
+D 10
+L 25
+U 20

src/day9/main.rs

@@ -0,0 +1,116 @@
+use std::collections::HashSet;
+use base::read_file;
+
+#[derive(Hash, Eq, PartialEq, Copy, Clone, Debug)]
+struct Position {
+    x: i32,
+    y: i32,
+}
+
+
+#[derive(Debug)]
+enum Direction {
+    UP,
+    DOWN,
+    LEFT,
+    RIGHT,
+}
+
+#[derive(Debug)]
+struct MoveCommand(Direction, i32);
+
+impl Position {
+    fn move_by(&mut self, dir: &Direction) {
+        match dir {
+            Direction::UP => self.y += 1,
+            Direction::DOWN => self.y -= 1,
+            Direction::LEFT => self.x -= 1,
+            Direction::RIGHT => self.x += 1
+        }
+    }
+
+    fn move_to(&mut self, other: &Position) {
+        if self.x > other.x {
+            self.x -= 1;
+        } else if self.x < other.x {
+            self.x += 1;
+        }
+
+        if self.y > other.y {
+            self.y -= 1;
+        } else if self.y < other.y {
+            self.y += 1;
+        }
+    }
+}
+
+struct Map<const N: usize> {
+    rope: [Position; N],
+    history: HashSet<Position>,
+}
+
+impl<const N: usize> Default for Map<N> {
+    fn default() -> Self {
+        assert!(N > 1, "Length must be larger than one");
+        Map {
+            rope: [Position { x: 0, y: 0 }; N],
+            history: Default::default(),
+        }
+    }
+}
+
+impl<const N: usize> Map<N> {
+    fn move_head(&mut self, cmd: &MoveCommand) {
+        for _ in 0..cmd.1 {
+            self.rope[0].move_by(&cmd.0);
+
+            for rope_element in 1..N {
+                if !self.is_in_reach(rope_element) {
+                    let element_before = self.rope[rope_element - 1];
+                    self.rope[rope_element].move_to(&element_before);
+                    if rope_element == N - 1 {
+                        self.history.insert(self.rope[rope_element]);
+                    }
+                }
+            }
+        }
+    }
+
+    fn is_in_reach(&self, which: usize) -> bool {
+        (self.rope[which - 1].x - self.rope[which].x).abs() <= 1 && (self.rope[which].y - self.rope[which - 1].y).abs() <= 1
+    }
+}
+
+fn main() {
+    let mut commands = vec![];
+
+    for line in read_file("day9.txt") {
+        let splits = line.split_whitespace().collect::<Vec<_>>();
+        let count = splits[1].parse::<i32>().unwrap();
+        commands.push(match splits[0] {
+            "U" => MoveCommand(Direction::UP, count),
+            "L" => MoveCommand(Direction::LEFT, count),
+            "D" => MoveCommand(Direction::DOWN, count),
+            "R" => MoveCommand(Direction::RIGHT, count),
+            _ => {
+                panic!("Unknown option")
+            }
+        });
+    }
+
+    let mut task_1 = Map::<2>::default();
+
+    for command in &commands {
+        task_1.move_head(command);
+    }
+
+    println!("Tail was at {} unique fields", task_1.history.len() + 1);
+
+    let mut task_2 = Map::<10>::default();
+
+    for command in &commands {
+        task_2.move_head(command);
+    }
+
+    println!("Tail was at {} unique fields", task_2.history.len() + 1);
+}