day6: complete solution + grid lib (used in solution)

6/Cargo.lock

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+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "day6"
+version = "0.1.0"
+dependencies = [
+ "grid",
+]
+
+[[package]]
+name = "grid"
+version = "0.1.0"

6/Cargo.toml

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+[package]
+name = "day6"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+grid = { version = "0.1.0", path = "../libs/grid" }

6/src/main.rs

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+use std::collections::{HashMap, HashSet};
+use std::fmt::Display;
+use std::fs::File;
+use std::io::{BufRead, BufReader, Lines};
+use std::time::{Duration, Instant};
+
+// BOILERPLATE
+type InputIter = Lines<BufReader<File>>;
+
+pub fn get_input() -> InputIter {
+    let f = File::open("input").unwrap();
+    let br = BufReader::new(f);
+    br.lines()
+}
+
+fn duration_format(duration: Duration) -> String {
+    match duration.as_secs_f64() {
+        x if x > 1.0 => format!("{:.3}s", x),
+        x if x > 0.010 => format!("{:.3}ms", x * 1e3),
+        x => format!("{:.3}us", x * 1e6),
+    }
+}
+
+fn main() {
+    let input = get_input();
+    let start = Instant::now();
+    let ans1 = problem1(input);
+    let duration1 = start.elapsed();
+    println!("Problem 1 solution: {} [{}]", ans1, duration_format(duration1));
+
+    let input = get_input();
+    let start = Instant::now();
+    let ans2 = problem2(input);
+    let duration2 = start.elapsed();
+    println!("Problem 2 solution: {} [{}]", ans2, duration_format(duration2));
+    println!("Total duration: {}", duration_format(duration1 + duration2));
+}
+
+#[repr(u8)]
+#[derive(Copy, Clone, Debug, Eq, PartialEq, Hash)]
+enum FacingDirection {
+    Up = b'^',
+    Down = b'v',
+    Left = b'<',
+    Right = b'>',
+}
+
+impl FacingDirection {
+    fn next(&self) -> FacingDirection {
+        match self {
+            FacingDirection::Up => FacingDirection::Right,
+            FacingDirection::Down => FacingDirection::Left,
+            FacingDirection::Left => FacingDirection::Up,
+            FacingDirection::Right => FacingDirection::Down,
+        }
+    }
+    fn pos_ofs(&self, pos: (i64, i64)) -> (i64, i64) {
+        match self {
+            FacingDirection::Up => (pos.0 + 0, pos.1 + -1),
+            FacingDirection::Down => (pos.0 + 0, pos.1 + 1),
+            FacingDirection::Left => (pos.0 + -1, pos.1 + 0),
+            FacingDirection::Right => (pos.0 + 1, pos.1 + 0),
+        }
+    }
+}
+
+enum StepOutcome {
+    LeftMap,
+    LoopFound,
+    Continue,
+}
+
+enum RunOutcome {
+    LeftMap,
+    LoopFound,
+    Stuck,
+}
+
+#[derive(Clone)]
+struct Map {
+    grid: grid::Grid<u8>,
+    visited_from: HashMap<(i64, i64), HashSet<FacingDirection>>,
+    guard_facing: FacingDirection,
+    guard_pos: (i64, i64),
+}
+
+impl<T: BufRead> From<Lines<T>> for Map {
+    fn from(input: Lines<T>) -> Self {
+        let grid = grid::Grid::from(input);
+        let visited_from = HashMap::new();
+        let guard_pos = grid.find(b'^').expect("Guard not found");
+        let guard_facing = FacingDirection::Up;
+        Self {
+            grid,
+            guard_pos,
+            guard_facing,
+            visited_from,
+        }
+    }
+}
+
+impl Map {
+    fn look(&self, dir: &FacingDirection) -> Option<u8> {
+        match dir {
+            FacingDirection::Up => self.grid.get(self.guard_pos.0, self.guard_pos.1 - 1),
+            FacingDirection::Down => self.grid.get(self.guard_pos.0, self.guard_pos.1 + 1),
+            FacingDirection::Left => self.grid.get(self.guard_pos.0 - 1, self.guard_pos.1),
+            FacingDirection::Right => self.grid.get(self.guard_pos.0 + 1, self.guard_pos.1),
+        }
+    }
+    /// Move one step in the facing direction, return if we are still inside the bounds
+    fn step_guard(&mut self) -> StepOutcome {
+        let new_pos = self.guard_facing.pos_ofs(self.guard_pos);
+        if self.visited_from.contains_key(&new_pos) && self.visited_from[&new_pos].contains(&self.guard_facing) {
+            return StepOutcome::LoopFound;
+        }
+        if self.grid.set(new_pos.0, new_pos.1, b'X') {
+            self.visited_from
+                .entry(new_pos)
+                .or_insert(HashSet::new())
+                .insert(self.guard_facing);
+            self.guard_pos = new_pos;
+            StepOutcome::Continue
+        } else {
+            StepOutcome::LeftMap
+        }
+    }
+    fn run_guard(&mut self) -> RunOutcome {
+        // if the guard is surrounded by obstacles, bail out
+        if self
+            .grid
+            .get(self.guard_pos.0 - 1, self.guard_pos.1)
+            .is_some_and(|v| v == b'#')
+            && self
+                .grid
+                .get(self.guard_pos.0 + 1, self.guard_pos.1)
+                .is_some_and(|v| v == b'#')
+            && self
+                .grid
+                .get(self.guard_pos.0, self.guard_pos.1 - 1)
+                .is_some_and(|v| v == b'#')
+            && self
+                .grid
+                .get(self.guard_pos.0, self.guard_pos.1 + 1)
+                .is_some_and(|v| v == b'#')
+        {
+            return RunOutcome::Stuck;
+        }
+        while let Some(val) = self.look(&self.guard_facing) {
+            match val {
+                b'#' => {
+                    // obstacle, turn right
+                    self.guard_facing = self.guard_facing.next();
+                }
+                _ => match self.step_guard() {
+                    StepOutcome::LeftMap => return RunOutcome::LeftMap,
+                    StepOutcome::LoopFound => return RunOutcome::LoopFound,
+                    StepOutcome::Continue => {}
+                },
+                
+            }
+        }
+        return RunOutcome::LeftMap;
+    }
+}
+
+// PROBLEM 1 solution
+
+fn problem1<T: BufRead>(input: Lines<T>) -> u64 {
+    let mut map = Map::from(input);
+    eprintln!("problem 1");
+    map.run_guard();
+
+    (map.grid.count(b'X') + map.grid.count(b'-') + map.grid.count(b'|') + map.grid.count(b'^')) as u64
+}
+
+// PROBLEM 2 solution
+fn problem2<T: BufRead>(input: Lines<T>) -> u64 {
+    let input_map = Map::from(input);
+    let mut loop_count = 0u64;
+    for y in 0..input_map.grid.height() {
+        for x in 0..input_map.grid.width() {
+            eprintln!("Replacing ({}, {}) with obstacle", x, y);
+            match input_map.grid.get(x as i64, y as i64) {
+                Some(b'.') => {
+                    let mut test_map = input_map.clone();
+                    test_map.grid.set(x as i64, y as i64, b'#');
+                    match test_map.run_guard() {
+                        RunOutcome::LoopFound => loop_count += 1,
+                        _ => {}
+                    }
+                }
+                _ => continue,
+            }
+        }
+    }
+    loop_count
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::*;
+    use std::io::Cursor;
+
+    const EXAMPLE: &str = &"....#.....
+.........#
+..........
+..#.......
+.......#..
+..........
+.#..^.....
+........#.
+#.........
+......#...";
+
+    #[test]
+    fn problem1_example() {
+        let c = Cursor::new(EXAMPLE);
+        assert_eq!(problem1(c.lines()), 41);
+    }
+
+    #[test]
+    fn problem2_example() {
+        let c = Cursor::new(EXAMPLE);
+        assert_eq!(problem2(c.lines()), 6);
+    }
+}