From 66ddb140f254513b4e38d9b4c9c80db77364f51b Mon Sep 17 00:00:00 2001
From: Justin Wernick <justin@worthe-it.co.za>
Date: Fri, 9 Dec 2022 08:03:56 +0200
Subject: Day 9

---
 2022/src/bin/day_9.rs | 134 ++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 134 insertions(+)
 create mode 100644 2022/src/bin/day_9.rs

(limited to '2022/src/bin/day_9.rs')

diff --git a/2022/src/bin/day_9.rs b/2022/src/bin/day_9.rs
new file mode 100644
index 0000000..ccbb66a
--- /dev/null
+++ b/2022/src/bin/day_9.rs
@@ -0,0 +1,134 @@
+use nom::{
+    branch::alt,
+    bytes::complete::tag,
+    character::complete::{i32, line_ending},
+    combinator::{map, value},
+    multi::separated_list1,
+    sequence::tuple,
+    IResult,
+};
+use std::{collections::BTreeSet, fs};
+
+fn main() -> Result<(), Box<dyn std::error::Error>> {
+    let input = fs::read_to_string("inputs/day_9.txt")?;
+    let movements = Movements::parser(&input).unwrap().1;
+
+    let mut game_board_part_1 = GameBoard::new(2);
+    for instruction in &movements.0 {
+        game_board_part_1.step(instruction);
+    }
+    dbg!(game_board_part_1.tail_visited.len());
+
+    let mut game_board_part_2 = GameBoard::new(10);
+    for instruction in &movements.0 {
+        game_board_part_2.step(instruction);
+    }
+    dbg!(game_board_part_2.tail_visited.len());
+
+    Ok(())
+}
+
+#[derive(Debug)]
+struct Movements(Vec<Instruction>);
+
+#[derive(Debug)]
+struct Instruction {
+    direction: Direction,
+    distance: i32,
+}
+
+#[derive(Debug, Clone, Copy)]
+enum Direction {
+    Down,
+    Up,
+    Left,
+    Right,
+}
+
+impl Movements {
+    fn parser(input: &str) -> IResult<&str, Self> {
+        map(separated_list1(line_ending, Instruction::parser), Movements)(input)
+    }
+}
+
+impl Instruction {
+    fn parser(input: &str) -> IResult<&str, Self> {
+        map(
+            tuple((Direction::parser, tag(" "), i32)),
+            |(direction, _, distance)| Instruction {
+                direction,
+                distance,
+            },
+        )(input)
+    }
+}
+
+impl Direction {
+    fn parser(input: &str) -> IResult<&str, Self> {
+        alt((
+            value(Direction::Down, tag("D")),
+            value(Direction::Up, tag("U")),
+            value(Direction::Left, tag("L")),
+            value(Direction::Right, tag("R")),
+        ))(input)
+    }
+}
+
+#[derive(Debug)]
+struct GameBoard {
+    rope: Vec<Position>,
+    tail_visited: BTreeSet<Position>,
+}
+
+#[derive(Default, Debug, PartialEq, Eq, PartialOrd, Ord, Clone)]
+struct Position {
+    x: i32,
+    y: i32,
+}
+
+impl GameBoard {
+    fn new(length: usize) -> GameBoard {
+        let mut tail_visited = BTreeSet::new();
+        tail_visited.insert(Position::default());
+        GameBoard {
+            rope: vec![Position::default(); length],
+            tail_visited,
+        }
+    }
+
+    fn step(&mut self, instruction: &Instruction) {
+        for _ in 0..instruction.distance {
+            match instruction.direction {
+                Direction::Down => self.rope[0].y -= 1,
+                Direction::Up => self.rope[0].y += 1,
+                Direction::Left => self.rope[0].x -= 1,
+                Direction::Right => self.rope[0].x += 1,
+            };
+
+            for tail_i in 1..self.rope.len() {
+                let head_i = tail_i - 1;
+                let head = self.rope[head_i].clone();
+                let tail = &mut self.rope[tail_i];
+
+                let tail_must_move = (head.x - tail.x).abs() > 1 || (head.y - tail.y).abs() > 1;
+
+                if tail_must_move {
+                    if head.x > tail.x {
+                        tail.x += 1;
+                    } else if head.x < tail.x {
+                        tail.x -= 1;
+                    }
+
+                    if head.y > tail.y {
+                        tail.y += 1;
+                    } else if head.y < tail.y {
+                        tail.y -= 1;
+                    }
+                }
+            }
+
+            self.tail_visited
+                .insert(self.rope[self.rope.len() - 1].clone());
+        }
+    }
+}
-- 
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