add day6

Author: mirsella

Diff for: 2024/Cargo.toml

@@ -6,7 +6,7 @@ members = [
   "day3",
   "day4",
   "day5",
-  # "day6",
+  "day6",
   # "day7",
   # "day8",
   # "day9",

Diff for: 2024/day6/.gitignore

@@ -0,0 +1,19 @@
+input.txt
+flamegraph.svg
+perf.data*
+### Rust
+# Generated by Cargo
+# will have compiled files and executables
+debug/
+target/
+
+# Remove Cargo.lock from gitignore if creating an executable, leave it for libraries
+# More information here https://doc.rust-lang.org/cargo/guide/cargo-toml-vs-cargo-lock.html
+Cargo.lock
+
+# These are backup files generated by rustfmt
+**/*.rs.bk
+
+# MSVC Windows builds of rustc generate these, which store debugging information
+*.pdb
+

Diff for: 2024/day6/Cargo.toml

@@ -0,0 +1,12 @@
+[package]
+name = "day6"
+authors = ["mirsella <[email protected]>"]
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+itertools = "0.13.0"
+pathfinding = "4.11.0"
+rayon = "1.10.0"

Diff for: 2024/day6/build.rs

@@ -0,0 +1,28 @@
+use std::fs::File;
+use std::io::{self, Read};
+use std::path::PathBuf;
+use std::{env, fs};
+
+fn replace_in_file(file_path: &PathBuf, old: &str, new: &str) -> io::Result<()> {
+    let mut contents = String::new();
+    File::open(file_path)?.read_to_string(&mut contents)?;
+    let new_contents = contents.replace(old, new);
+    if contents != new_contents {
+        println!("Updating {}", file_path.display());
+        fs::write(file_path, new_contents)?;
+    }
+    Ok(())
+}
+
+fn main() -> io::Result<()> {
+    let pkg_name = env::var("CARGO_PKG_NAME").unwrap();
+    replace_in_file(
+        &"../Cargo.toml".into(),
+        &format!("# \"{pkg_name}\""),
+        &format!("\"{pkg_name}\""),
+    )?;
+
+    replace_in_file(&"./Cargo.toml".into(), "\n[workspace]", "")?;
+
+    Ok(())
+}

Diff for: 2024/day6/src/main.rs

@@ -0,0 +1,156 @@
+use itertools::Itertools;
+use pathfinding::matrix::{directions::*, Matrix};
+use rayon::prelude::*;
+use std::collections::HashSet;
+
+fn part1(input: &str) -> usize {
+    let directions = [(N, '^'), (E, '>'), (S, 'v'), (W, '<')];
+    let get_direction = |char: char| directions.iter().find(|(_, c)| char == *c).unwrap().0;
+    let get_next_direction =
+        |char: char| directions[(directions.iter().position(|v| char == v.1).unwrap() + 1) % 4];
+    let mut m = Matrix::from_rows(input.lines().map(str::chars)).unwrap();
+    let mut pos = m
+        .items()
+        .find_map(|(p, c)| directions.iter().any(|dir| dir.1 == *c).then_some(p))
+        .unwrap();
+    loop {
+        let Some((newpos, new)) = m
+            .move_in_direction(pos, get_direction(m[pos]))
+            .map(|p| (p, m[p]))
+        else {
+            break;
+        };
+        if new == '#' {
+            m[pos] = get_next_direction(m[pos]).1
+        } else {
+            m[newpos] = m[pos];
+            pos = newpos;
+        }
+    }
+    m.values()
+        .filter(|&&c| directions.iter().any(|dir| dir.1 == c))
+        .count()
+}
+
+// try to do it without bruteforce
+fn _part2_clever(input: &str) -> usize {
+    let directions = [(N, '^'), (E, '>'), (S, 'v'), (W, '<')];
+    let get_direction = |char: char| directions.iter().find(|(_, c)| char == *c).unwrap().0;
+    let get_next_direction =
+        |char: char| directions[(directions.iter().position(|v| char == v.1).unwrap() + 1) % 4];
+    let mut m = Matrix::from_rows(input.lines().map(str::chars)).unwrap();
+    let mut pos = m
+        .items()
+        .find_map(|(p, c)| directions.iter().any(|dir| dir.1 == *c).then_some(p))
+        .unwrap();
+    let start = pos;
+    let mut possible_obstructions = HashSet::new();
+    loop {
+        let direction = get_direction(m[pos]);
+        let Some((newpos, new)) = m.move_in_direction(pos, direction).map(|p| (p, m[p])) else {
+            break;
+        };
+        let next_direction = get_next_direction(m[pos]);
+        if new == '#' {
+            m[pos] = next_direction.1;
+        } else {
+            m[newpos] = m[pos];
+            pos = newpos;
+            // if putting a obstruction at the new tile will make the guard join a path he already took
+            let next_next_direction = get_next_direction(next_direction.1);
+            for tile in m.in_direction(pos, get_next_direction(m[pos]).0) {
+                if m[tile] == next_direction.1
+                    || (m[tile] == next_next_direction.1
+                        && m[m.move_in_direction(tile, next_direction.0).unwrap()] == '#')
+                {
+                    let move_in_direction = m.move_in_direction(pos, direction).unwrap();
+                    if move_in_direction != start {
+                        possible_obstructions.insert(move_in_direction);
+                    }
+                    break;
+                }
+            }
+        }
+    }
+    for pos in possible_obstructions.iter() {
+        m[*pos] = 'O'
+    }
+    for row in m.iter() {
+        println!("{}", row.iter().collect::<String>());
+    }
+    possible_obstructions.len()
+}
+
+// bruteforce but thanks to rayon its still ~250ms to run
+fn part2(input: &str) -> usize {
+    let directions = [(N, '^'), (E, '>'), (S, 'v'), (W, '<')];
+    let get_direction = |char: char| directions.iter().find(|(_, c)| char == *c).unwrap().0;
+    let get_next_direction =
+        |char: char| directions[(directions.iter().position(|v| char == v.1).unwrap() + 1) % 4];
+    let m = Matrix::from_rows(input.lines().map(str::chars)).unwrap();
+    let pos = m
+        .items()
+        .find_map(|(p, c)| directions.iter().any(|dir| dir.1 == *c).then_some(p))
+        .unwrap();
+    let is_infinite = |mut m: Matrix<char>, mut pos: (usize, usize)| -> bool {
+        let mut seen = HashSet::new();
+        loop {
+            let direction = get_direction(m[pos]);
+            let Some((newpos, new)) = m.move_in_direction(pos, direction).map(|p| (p, m[p])) else {
+                break;
+            };
+            let next_direction = get_next_direction(m[pos]);
+            if new == '#' {
+                m[pos] = next_direction.1;
+            } else {
+                m[newpos] = m[pos];
+                pos = newpos;
+                if !seen.insert((pos, m[pos])) {
+                    return true;
+                }
+            }
+        }
+        false
+    };
+    m.keys()
+        .collect_vec()
+        .par_iter()
+        .filter(|&&tile| {
+            if tile == pos {
+                return false;
+            }
+            let mut m = m.clone();
+            m[tile] = '#';
+            is_infinite(m, pos)
+        })
+        .count()
+}
+
+fn main() {
+    let input = include_str!("../input.txt");
+    println!("Part 1: {}", part1(input));
+    println!("Part 2: {}", part2(input));
+}
+
+#[cfg(test)]
+mod tests {
+    const INPUT: &str = "....#.....
+.........#
+..........
+..#.......
+.......#..
+..........
+.#..^.....
+........#.
+#.........
+......#...
+";
+    #[test]
+    fn part1() {
+        assert_eq!(super::part1(INPUT), 41);
+    }
+    #[test]
+    fn part2() {
+        assert_eq!(super::part2(INPUT), 6);
+    }
+}

Diff for: template/cargo-generate.toml

@@ -9,6 +9,6 @@ prompt = "example input equal to"
 regex = "[0-9]+"
 
 [placeholders.input]
-type = "text"
+type = "editor"
 prompt = "main puzzle input"
 regex = "[^ ]"