Add day6

2024/day6/.gitignore

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+target
+input.txt

2024/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"

2024/day6/Cargo.toml

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

2024/day6/src/main.rs

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+use std::collections::{HashMap, HashSet};
+use std::fs;
+use std::time::Instant;
+
+#[derive(Debug, PartialEq, Eq, Hash, Clone, Copy)]
+struct Point {
+    row: i32,
+    col: i32,
+}
+
+impl Point {
+    fn new(row: i32, col: i32) -> Self {
+        Self { row, col }
+    }
+
+    fn from(point: &Point, dir: &Point) -> Self {
+        Self {
+            row: point.row + dir.row,
+            col: point.col + dir.col,
+        }
+    }
+
+    fn is_in_map(&self, map: &[&[u8]]) -> bool {
+        !(self.col >= map[0].len() as i32
+            || self.row >= map.len() as i32
+            || self.col < 0
+            || self.row < 0)
+    }
+
+    fn is_in_map_str(&self, map: &[String]) -> bool {
+        !(self.col >= map[0].len() as i32
+            || self.row >= map.len() as i32
+            || self.col < 0
+            || self.row < 0)
+    }
+}
+
+const DIRECTION: [Point; 4] = [
+    Point { row: 1, col: 0 },
+    Point { row: 0, col: -1 },
+    Point { row: -1, col: 0 },
+    Point { row: 0, col: 1 },
+];
+
+fn main() {
+    let file = fs::read_to_string("./input.txt").unwrap();
+
+    let mut map: Vec<&[u8]> = Vec::new();
+    let mut map2: Vec<String> = Vec::new();
+    let mut start = Point::new(0, 0);
+
+    for (line_idx, line) in file.lines().enumerate() {
+        map.push(line.as_bytes());
+        map2.push(line.to_string());
+        for (idx, c) in line.chars().enumerate() {
+            if c == '^' {
+                start.row = line_idx as i32;
+                start.col = idx as i32;
+            }
+        }
+    }
+
+    let start_time = Instant::now();
+    println!("Solution 1: {}", puzzle1(map.clone(), start));
+    let end = Instant::now() - start_time;
+    println!("Solution 1 time: {}", end.as_micros());
+
+    let start_time = Instant::now();
+    println!("Solution 2: {}", puzzle2(map2, start));
+    let end = Instant::now() - start_time;
+    println!("Solution 2 time: {}", end.as_micros());
+}
+
+fn puzzle1(map: Vec<&[u8]>, start: Point) -> usize {
+    let mut visited = HashSet::new();
+    visited.insert(start);
+    let mut current = start;
+    let mut dir = 2;
+
+    loop {
+        let next = Point::from(&current, &DIRECTION[dir]);
+        if !next.is_in_map(&map) {
+            break;
+        }
+        if map[next.row as usize][next.col as usize] != b'#' {
+            visited.insert(next);
+            current = next;
+        } else {
+            dir = (dir + 1) % 4;
+        }
+    }
+    visited.len()
+}
+
+fn puzzle2(map: Vec<String>, start: Point) -> usize {
+    let mut map = map;
+    let visited = HashMap::new();
+    let mut positions = HashSet::new();
+    puzzle2_rec(start, 2, &mut map, visited, &mut positions, false);
+
+    positions.len()
+}
+
+fn puzzle2_rec(
+    mut current: Point,
+    mut dir: usize,
+    map: &mut Vec<String>,
+    mut visited: HashMap<Point, [bool; 4]>,
+    positions: &mut HashSet<Point>,
+    placed: bool,
+) -> bool {
+    while current.is_in_map_str(map) {
+        visited
+            .entry(current)
+            .or_insert([false, false, false, false]);
+        if visited[&current][dir] && placed {
+            return true;
+        }
+        let next = Point::from(&current, &DIRECTION[dir]);
+        if !next.is_in_map_str(map) {
+            return false;
+        }
+        if map[next.row as usize].as_bytes()[next.col as usize] == b'#' {
+            dir = (dir + 1) % 4;
+        } else {
+            if !placed && !visited.contains_key(&next) {
+                let c = map[next.row as usize]
+                    .chars()
+                    .nth(next.col as usize)
+                    .unwrap();
+                map[next.row as usize].replace_range(next.col as usize..=next.col as usize, "#");
+                if puzzle2_rec(
+                    current,
+                    (dir + 1) % 4,
+                    map,
+                    visited.clone(),
+                    positions,
+                    true,
+                ) {
+                    positions.insert(next);
+                }
+                map[next.row as usize]
+                    .replace_range(next.col as usize..=next.col as usize, &c.to_string());
+            }
+            visited.get_mut(&current).unwrap()[dir] = true;
+            current = next;
+        }
+    }
+    false
+}