day09 in progress.

days/day09/Cargo.toml

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+[package]
+name = "day09"
+authors.workspace = true
+description.workspace = true
+version.workspace = true

days/day09/src/main.rs

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+//TODO:
+#![allow(dead_code)]
+mod part1;
+mod part2;
+mod parse;
+mod rope;
+
+fn main() {
+    let input = include_str!("./input.txt");
+    let structured_input = parse::parse(input);
+
+    println!("Part One");
+    println!("Result: {}", part1::part1());
+
+    println!("Part Two");
+    println!("Result: {}", part2::part2());
+}

days/day09/src/parse.rs

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+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum Direction {
+    Up,
+    Right,
+    Down,
+    Left,
+}
+
+pub fn parse(input: &str) -> Vec<Direction> {
+    let mut ret = Vec::new();
+    for line in input.lines() {
+        let mut chars = line.chars();
+        let dir = match chars.next().unwrap() {
+            'U' => Direction::Up,
+            'R' => Direction::Right,
+            'D' => Direction::Down,
+            'L' => Direction::Left,
+            _ => panic!("invalid direction char"),
+        };
+        for _ in 0..chars.nth(1).unwrap().to_digit(10).unwrap() {
+            ret.push(dir)
+        }
+    }
+    ret
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_parse() {
+        let input =
+            concat!("R 4\n", "U 4\n", "L 3\n", "D 1\n", "R 4\n", "D 1\n", "L 5\n", "R 2\n",);
+        assert_eq!(
+            parse(input),
+            vec![
+                Direction::Right,
+                Direction::Right,
+                Direction::Right,
+                Direction::Right,
+                Direction::Up,
+                Direction::Up,
+                Direction::Up,
+                Direction::Up,
+                Direction::Left,
+                Direction::Left,
+                Direction::Left,
+                Direction::Down,
+                Direction::Right,
+                Direction::Right,
+                Direction::Right,
+                Direction::Right,
+                Direction::Down,
+                Direction::Left,
+                Direction::Left,
+                Direction::Left,
+                Direction::Left,
+                Direction::Left,
+                Direction::Right,
+                Direction::Right,
+            ]
+        );
+    }
+}

days/day09/src/part1.rs

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+//TODO:
+#![allow(unused)]
+
+pub fn part1() -> usize {
+    unimplemented!()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_part1() {
+        assert_eq!(0, 0);
+    }
+}

days/day09/src/part2.rs

@@ -0,0 +1,16 @@
+//TODO:
+#![allow(unused)]
+
+pub fn part2() -> usize {
+    unimplemented!()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_part2() {
+        assert_eq!(0, 0);
+    }
+}

days/day09/src/rope.rs

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+use crate::parse::Direction;
+#[derive(Debug, Clone, Copy)]
+struct Point {
+    x: isize,
+    y: isize,
+}
+
+impl std::ops::Add for Point {
+    type Output = Point;
+
+    fn add(self, rhs: Self) -> Self::Output {
+        Self {
+            x: self.x + rhs.x,
+            y: self.y + rhs.y,
+        }
+    }
+}
+
+impl std::ops::Sub for Point {
+    type Output = Point;
+
+    fn sub(self, rhs: Self) -> Self::Output {
+        Self {
+            x: self.x - rhs.x,
+            y: self.y - rhs.y,
+        }
+    }
+}
+
+// L is the length of the rope in segments.
+#[derive(Debug)]
+struct Rope<const L: usize> {
+    segments: [Point; L],
+}
+
+impl<const L: usize> Rope<L> {
+    pub fn new()->Rope{
+        Rope { segments: () }
+    }
+
+    pub fn update_rope(&mut self, direction: Direction) {
+        todo!()
+    }
+
+    pub fn get_tail_pos(&self)->&Point{
+        &self.segments[self.segments.len()-1]
+    }
+
+    fn update_single_segment_pair(head: Point, tail: Point) -> Point {
+        let delta = head - tail;
+        if delta.x.abs() > 2 || delta.y.abs() > 2 {
+            panic!("invalid delta ({}, {})", delta.y, delta.x)
+        }
+        match (delta.x, delta.y) {
+            (0, 2) => Point { x: 0, y: 1 },
+            (2, 0) => Point { x: 1, y: 0 },
+            (0, -2) => Point { x: 0, y: -1 },
+            (-2, 0) => Point { x: -1, y: 0 },
+            (1, 2) | (2, 2) | (2, 1) => Point { x: 1, y: 1 },
+            (2, -1) | (2, -2) | (1, -2) => Point { x: 1, y: -1 },
+            (-1, -2) | (-2, -2) | (-2, -1) => Point { x: -1, y: -1 },
+            (-2, 1) | (-2, 2) | (-1, 2) => Point { x: -1, y: 1 },
+            _ => Point { x: 0, y: 0 },
+        }
+    }
+}