Add solutions for day 6.1

inputs/day_6.txt

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src/main.rs

@@ -18,6 +18,7 @@ fn main() -> std::io::Result<()> {
         Ok(3) => solutions::day_3::run(args)?,
         Ok(4) => solutions::day_4::run(args)?,
         Ok(5) => solutions::day_5::run(args)?,
+        Ok(6) => solutions::day_6::run(args)?,
         Ok(_) => eprintln!("Unknown day. Are you from the future?"),
         Err(_) => eprintln!("Unknown day format. Use integers to specify."),
     }

src/solutions/day_6.rs

@@ -0,0 +1,153 @@
+use std::env;
+use std::fs::File;
+use std::io::{BufRead, BufReader};
+
+#[derive(Copy, Clone, Debug, PartialEq)]
+enum Field {
+    Obstacle,
+    Unvisited,
+    Visited,
+}
+
+impl Field {
+    fn blocked(&self) -> bool {
+        *self == Field::Obstacle
+    }
+}
+
+#[derive(Copy, Clone, Debug)]
+enum Direction {
+    Up,
+    Right,
+    Down,
+    Left,
+}
+
+impl Into<Direction> for char {
+    fn into(self) -> Direction {
+        match self {
+            '^' => Direction::Up,
+            '>' => Direction::Right,
+            'v' => Direction::Down,
+            '<' => Direction::Left,
+            _ => panic!("Unknown direction {self}"),
+        }
+    }
+}
+
+struct Guard {
+    pub x: usize,
+    pub y: usize,
+    pub dir: Direction,
+}
+
+pub fn run(mut args: env::Args) -> std::io::Result<()> {
+    let filename = args
+        .next()
+        .expect("You must provide a filename as argument");
+
+    let f = File::open(filename)?;
+    let reader = BufReader::new(f);
+
+    let mut map: Vec<Vec<Field>> = Vec::new();
+    let mut guard: Guard = Guard {
+        x: 0,
+        y: 0,
+        dir: Direction::Up,
+    };
+
+    let mut y = 0;
+    for line in reader.lines() {
+        let l = line.unwrap();
+
+        map.push(
+            l.chars()
+                .enumerate()
+                .map(|(idx, c)| match c {
+                    '.' => Field::Unvisited,
+                    '#' => Field::Obstacle,
+                    '^' | '>' | 'v' | '<' => {
+                        guard.y = y;
+                        guard.x = idx;
+                        guard.dir = c.into();
+                        Field::Visited
+                    }
+                    _ => panic!("Illegal field formatter: '{c}'"),
+                })
+                .collect(),
+        );
+
+        y += 1;
+    }
+
+    // simulate guard movement
+    loop {
+        match guard.dir {
+            Direction::Up => {
+                if guard.y == 0 {
+                    break;
+                } else {
+                    if map[guard.y - 1][guard.x].blocked() {
+                        guard.dir = Direction::Right;
+                        continue;
+                    } else {
+                        guard.y -= 1;
+                    }
+                }
+            }
+            Direction::Right => {
+                if (guard.x + 1) == map[guard.y].len() {
+                    break;
+                } else {
+                    if map[guard.y][guard.x + 1].blocked() {
+                        guard.dir = Direction::Down;
+                        continue;
+                    } else {
+                        guard.x += 1;
+                    }
+                }
+            }
+            Direction::Down => {
+                if (guard.y + 1) == map.len() {
+                    break;
+                } else {
+                    if map[guard.y + 1][guard.x].blocked() {
+                        guard.dir = Direction::Left;
+                        continue;
+                    } else {
+                        guard.y += 1
+                    }
+                }
+            }
+            Direction::Left => {
+                if guard.x == 0 {
+                    break;
+                } else {
+                    if map[guard.y][guard.x - 1].blocked() {
+                        guard.dir = Direction::Up;
+                        continue;
+                    } else {
+                        guard.x -= 1
+                    }
+                }
+            }
+        }
+
+        // if we haven't exited yet we must update the field
+        map[guard.y][guard.x] = Field::Visited;
+    }
+
+    // Task 1
+    let sum_visited = map.iter().fold(0, |acc, v| {
+        v.iter().fold(
+            acc,
+            |a, elem| if *elem == Field::Visited { a + 1 } else { a },
+        )
+    });
+    println!("Sum of visited fields: {sum_visited}");
+
+    // Task 2
+    // TODO
+
+    Ok(())
+}

src/solutions/mod.rs

@@ -3,4 +3,5 @@ pub mod day_2;
 pub mod day_3;
 pub mod day_4;
 pub mod day_5;
+pub mod day_6;