Day 6

src/day6.rs

@@ -0,0 +1,124 @@
+use std::collections::HashSet;
+
+#[derive(PartialEq, Eq)]
+enum Position {
+    Occupied,
+    Free,
+}
+
+#[derive(Clone, Copy, PartialEq, Eq, Hash)]
+enum Direction {
+    Up,
+    Down,
+    Left,
+    Right,
+}
+
+impl Direction {
+    fn rotate(self) -> Self {
+        match self {
+            Self::Up => Self::Right,
+            Self::Right => Self::Down,
+            Self::Down => Self::Left,
+            Self::Left => Self::Up,
+        }
+    }
+
+    fn next(
+        self,
+        mut current: (usize, usize),
+        dimentions: (usize, usize),
+    ) -> Option<(usize, usize)> {
+        match self {
+            Self::Up => current.0 = current.0.checked_sub(1)?,
+            Self::Down => current.0 += 1,
+            Self::Left => current.1 = current.1.checked_sub(1)?,
+            Self::Right => current.1 += 1,
+        }
+        if current.0 >= dimentions.0 || current.1 >= dimentions.1 {
+            return None;
+        }
+        Some(current)
+    }
+}
+
+fn parse_board(data: &str) -> (Vec<Vec<Position>>, (usize, usize)) {
+    let mut position = None;
+    let board = data
+        .lines()
+        .enumerate()
+        .map(|(i, line)| {
+            line.bytes()
+                .enumerate()
+                .map(|(j, b)| match b {
+                    b'#' => Position::Occupied,
+                    b'.' => Position::Free,
+                    b'^' => {
+                        position = Some((i, j));
+                        Position::Free
+                    }
+                    byte => unreachable!("{}", byte as char),
+                })
+                .collect()
+        })
+        .collect();
+    (board, position.expect("User pos not found"))
+}
+
+fn get_visited(board: &[Vec<Position>], mut pos: (usize, usize)) -> HashSet<(usize, usize)> {
+    let mut visited = HashSet::new();
+    let mut direction = Direction::Up;
+    let dimentions = (board.len(), board[1].len());
+    loop {
+        let Some(p) = direction.next(pos, dimentions) else {
+            break;
+        };
+        if board[p.0][p.1] == Position::Occupied {
+            direction = direction.rotate();
+            continue;
+        }
+        pos = p;
+        visited.insert(p);
+    }
+    visited
+}
+
+pub fn task1() {
+    let (board, pos) = parse_board(&std::fs::read_to_string("input.txt").unwrap());
+    let mut visited = get_visited(&board, pos);
+    visited.insert(pos);
+    println!("{}", visited.len());
+}
+
+fn is_loop(board: &[Vec<Position>], mut pos: (usize, usize)) -> bool {
+    let mut visited = HashSet::new();
+    let mut direction = Direction::Up;
+    let dimentions = (board.len(), board[1].len());
+    loop {
+        let Some(p) = direction.next(pos, dimentions) else {
+            return false;
+        };
+        if board[p.0][p.1] == Position::Occupied {
+            direction = direction.rotate();
+            continue;
+        }
+        pos = p;
+        if !visited.insert((pos, direction)) {
+            return true;
+        }
+    }
+}
+
+pub fn task2() {
+    let (mut board, pos) = parse_board(&std::fs::read_to_string("input.txt").unwrap());
+    let visited = get_visited(&board, pos);
+    let mut c: usize = 0;
+    for (a, b) in visited {
+        board[a][b] = Position::Occupied;
+        if is_loop(&board, pos) {
+            c += 1;
+        }
+        board[a][b] = Position::Free;
+    }
+    println!("{c}");
+}

src/main.rs

@@ -3,6 +3,7 @@ mod day2;
 mod day3;
 mod day4;
 mod day5;
+mod day6;
 
 use std::{
     fs::File,
@@ -20,6 +21,6 @@ fn parse_line(line: &str, pattern: char) -> impl Iterator<Item = i32> + '_ {
 }
 
 fn main() {
-    day5::task1();
+    day6::task1();
-    day5::task2();
+    day6::task2();
 }