initial commit

day6/.gitignore

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+/target

day6/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"

day6/Cargo.toml

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+[package]
+name = "day6"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]

day6/input

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+........#........................................#......#........#................................................................
+....................................#......#.....#............#.............#..........#..........................................
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+...#...............................#.....#......#............###.#.#.....................................#....#.............#.....
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+............#..........................................#.....#.............#..........................#....................#.....#
+........................#......#..#............................#.......................................................#..........
+..#...#...#.......#.#..........................................#.............#.........#....#..................#...........#......
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+......##................#...........................................#..............##.................................#...........
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+.........................#..#...............#............................#.............#..........................#..............#

day6/src/main.rs

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+use std::fs::File;
+use std::io::{self, BufRead};
+use std::collections::{HashMap, HashSet};
+
+fn main() {
+    let file = File::open("input").unwrap();
+    let mut obstacles: HashSet<(i16, i16)> = HashSet::new();
+    let mut size_x: i16 = 0;
+    let mut size_y: i16 = 0;
+    let mut start_pos: (i16, i16) = (-1, -1);
+
+    for (line_idx, line_result) in io::BufReader::new(file).lines().enumerate() {
+        size_y += 1;
+        let line = match line_result {
+            Ok(content) => content,
+            Err(e) => {
+                eprintln!("Error reading line: {}", e);
+                continue;
+            }
+        };
+        
+        let mut line_size_x: i16 = 0;
+        for (i, c) in line.chars().enumerate() {
+            line_size_x += 1;
+            if c == '^' {
+                start_pos = (i.try_into().unwrap(), line_idx.try_into().unwrap());
+            }
+            if c == '#' {
+                obstacles.insert((i.try_into().unwrap(), line_idx.try_into().unwrap()));
+            }
+        }
+        if line_size_x > size_x {
+            size_x = line_size_x;
+        }
+    };
+
+    let visited_positions = run(&obstacles, start_pos, size_x, size_y);
+    println!("The guard visited {} distinct positions", visited_positions.unwrap());
+
+    let mut effective_obstructions: u16 = 0;
+    for x in 0..size_x {
+        for y in 0..size_y {
+            let mut obstacles_new = obstacles.clone();
+            obstacles_new.insert((x, y));
+            match run(&obstacles_new, start_pos, size_x, size_y) {
+                Some(_) => {},
+                None => effective_obstructions += 1,
+            }
+        }
+    }
+    println!("Effective obstructions: {}", effective_obstructions);
+}
+
+fn run(
+    obstacles: &HashSet<(i16, i16)>,
+    start_pos: (i16, i16),
+    size_x: i16,
+    size_y: i16,
+) -> Option<usize>
+{
+    #[derive(Copy, Clone, Eq, PartialEq, Hash)]
+    enum Direction {
+        Up,
+        Down,
+        Left,
+        Right,
+    }
+    let mut guard_pos: (i16, i16) = start_pos;
+    let mut direction: Direction = Direction::Up;
+    let mut visited: HashMap<(i16, i16), HashSet<Direction>> = HashMap::new();
+    loop {
+        let new_position = match direction {
+            Direction::Up => (guard_pos.0, guard_pos.1 - 1),
+            Direction::Down => (guard_pos.0, guard_pos.1 + 1),
+            Direction::Left => (guard_pos.0 - 1, guard_pos.1),
+            Direction::Right => (guard_pos.0 + 1, guard_pos.1),
+        };
+        if new_position.0 < 0 || new_position.0 > size_x || new_position.1 < 0 || new_position.1 > size_y {
+            break;
+        }
+
+
+        /*
+        visited
+            .entry(guard_pos)
+            .or_insert_with(HashSet::new)
+            .insert(direction);
+        */
+
+        if let Some(directions) = visited.get_mut(&guard_pos) {
+            if !directions.contains(&direction) {
+                directions.insert(direction);
+            } else {
+                return None;
+            }
+        } else {
+            let mut new_set = HashSet::new();
+            new_set.insert(direction);
+            visited.insert(guard_pos, new_set);
+        }
+
+        if obstacles.contains(&new_position) {
+            direction = match direction {
+                Direction::Up => Direction::Right,
+                Direction::Down => Direction::Left,
+                Direction::Left => Direction::Up,
+                Direction::Right => Direction::Down
+            };
+        }
+        else {
+            guard_pos = new_position;
+        }
+    }
+    Some(visited.keys().len())
+}