2 files changed, 110 insertions, 2 deletions
diff --git a/src/bin/day2.rs b/src/bin/day2.rs
new file mode 100644
index 0000000..066301f
--- /dev/null
+++ b/src/bin/day2.rs
@@ -0,0 +1,102 @@
+struct Position {
+    x: i32,
+    y: i32,
+}
+
+struct AimedPosition {
+    pos: Position,
+    aim: i32,
+}
+
+fn main() {
+    let input = advent::read_lines(2);
+
+    let pos = drive_course(Position {x: 0, y: 0}, &input);
+    println!("2a: {}", pos.x * pos.y);
+
+    let pos = drive_course_aimed(Position {x: 0, y: 0}, &input);
+    println!("2b: {}", pos.x * pos.y);
+}
+
+fn move_submarine(pos: Position, cmd: &str) -> Position {
+    let tokens : Vec<&str> = cmd.split(' ').collect();
+    let direction = tokens[0];
+    let distance = tokens[1].parse::<i32>().unwrap();
+
+    let mut pos = pos;
+    match direction {
+        "forward" => {
+            pos.x += distance;
+        },
+        "down" => {
+            pos.y += distance;
+        },
+        "up" => {
+            pos.y -= distance;
+        },
+        _ => panic!("invalid direction: {}", direction)
+    };
+
+    pos
+}
+
+fn move_submarine_aimed(pos: AimedPosition, cmd: &str) -> AimedPosition {
+    let tokens : Vec<&str> = cmd.split(' ').collect();
+    let direction = tokens[0];
+    let distance = tokens[1].parse::<i32>().unwrap();
+
+    let mut pos = pos;
+    match direction {
+        "forward" => {
+            pos.pos.x += distance;
+            pos.pos.y += pos.aim * distance;
+        },
+        "down" => {
+            pos.aim += distance;
+        },
+        "up" => {
+            pos.aim -= distance;
+        },
+        _ => panic!("invalid direction: {}", direction)
+    };
+
+    pos
+}
+
+fn drive_course<T: AsRef<str>>(start: Position, course: &[T]) -> Position {
+    let mut pos = start;
+    for cmd in course {
+        pos = move_submarine(pos, cmd.as_ref());
+    }
+    pos
+}
+
+fn drive_course_aimed<T: AsRef<str>>(start: Position, course: &[T]) -> Position {
+    let mut pos = AimedPosition { pos: start, aim: 0 };
+    for cmd in course {
+        pos = move_submarine_aimed(pos, cmd.as_ref());
+    }
+    pos.pos
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test() {
+        let course = [
+            "forward 5",
+            "down 5",
+            "forward 8",
+            "up 3",
+            "down 8",
+            "forward 2",
+        ];
+        let pos = drive_course(Position {x: 0, y: 0}, &course);
+        assert_eq!(pos.x * pos.y, 150);
+
+        let pos = drive_course_aimed(Position {x: 0, y: 0}, &course);
+        assert_eq!(pos.x * pos.y, 900);
+    }
+}
diff --git a/src/lib.rs b/src/lib.rs
index 6befee8..2f99150 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -4,9 +4,15 @@ pub fn read_file(day: u8) -> String {
     std::fs::read_to_string(filename).unwrap()
 }
 
-pub fn read_numbers(day: u8) -> Vec<usize> {
+pub fn read_lines(day: u8) -> Vec<String> {
     read_file(day).split('\n')
                   .filter(|n| !n.is_empty())
-                  .map(|n| n.parse::<usize>().unwrap())
+                  .map(String::from)
                   .collect()
 }
+
+pub fn read_numbers(day: u8) -> Vec<usize> {
+    read_lines(day).iter()
+                   .map(|n| n.parse::<usize>().unwrap())
+                   .collect()
+}