From f2ee9efbb4855a8ab4bf939896f5fb76da435465 Mon Sep 17 00:00:00 2001
From: Louis Vallat <contact@louis-vallat.dev>
Date: Sat, 7 Dec 2024 23:47:05 +0100
Subject: [PATCH] feat: added day 6 part 1 and 2

Signed-off-by: Louis Vallat <contact@louis-vallat.dev>
---
 .gitea/workflows/build_and_run.yml |   2 +-
 day6/Cargo.toml                    |   6 ++
 day6/src/main.rs                   | 140 +++++++++++++++++++++++++++++
 3 files changed, 147 insertions(+), 1 deletion(-)
 create mode 100644 day6/Cargo.toml
 create mode 100644 day6/src/main.rs

diff --git a/.gitea/workflows/build_and_run.yml b/.gitea/workflows/build_and_run.yml
index e0c67b5..b050cac 100644
--- a/.gitea/workflows/build_and_run.yml
+++ b/.gitea/workflows/build_and_run.yml
@@ -11,7 +11,7 @@ jobs:
     name: Challenge for day
     strategy:
       matrix:
-        day_number: [1, 2, 3, 4, 5]
+        day_number: [1, 2, 3, 4, 5, 6]
     runs-on: rust-bookworm
     steps:
       - name: Check out repository code
diff --git a/day6/Cargo.toml b/day6/Cargo.toml
new file mode 100644
index 0000000..46c0229
--- /dev/null
+++ b/day6/Cargo.toml
@@ -0,0 +1,6 @@
+[package]
+name = "day6"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
diff --git a/day6/src/main.rs b/day6/src/main.rs
new file mode 100644
index 0000000..09e286f
--- /dev/null
+++ b/day6/src/main.rs
@@ -0,0 +1,140 @@
+use std::collections::HashSet;
+use std::{env, fs};
+
+const DIRECTIONS: [(i32, i32); 4] = [(-1, 0), (0, 1), (1, 0), (0, -1)];
+
+#[derive(Clone, Eq, PartialEq)]
+enum Position {
+    Obstacle,
+    Visited(HashSet<usize>),
+    Free,
+}
+
+fn read_input(path: &str) -> String {
+    fs::read_to_string(path).expect("Cannot read file.")
+}
+
+fn parse_input(input: &str) -> (Vec<Vec<Position>>, (i32, i32)) {
+    let mut position = (0, 0);
+    let map = input
+        .lines()
+        .filter(|line| !line.is_empty())
+        .enumerate()
+        .map(|(row, line)| {
+            line.chars()
+                .enumerate()
+                .map(|(col, chr)| match chr {
+                    '#' => Position::Obstacle,
+                    '.' => Position::Free,
+                    '^' => {
+                        position = (row as i32, col as i32);
+                        Position::Visited(HashSet::from_iter(vec![0]))
+                    }
+                    _ => unreachable!("Invalid character in input"),
+                })
+                .collect()
+        })
+        .collect();
+
+    (map, position)
+}
+
+fn is_in_map(map: &Vec<Vec<Position>>, pos: (i32, i32)) -> bool {
+    (0..map.len() as i32).contains(&pos.0) && (0..map[pos.0 as usize].len() as i32).contains(&pos.1)
+}
+
+fn will_loop(map: &Vec<Vec<Position>>, mut pos: (i32, i32), mut current_direction: usize) -> bool {
+    let mut map = map.clone();
+    loop {
+        let direction = DIRECTIONS[current_direction];
+        let next_pos = (pos.0 + direction.0, pos.1 + direction.1);
+
+        if !is_in_map(&map, next_pos) {
+            break;
+        }
+
+        match &map[next_pos.0 as usize][next_pos.1 as usize] {
+            Position::Obstacle => {
+                current_direction = (current_direction + 1) % DIRECTIONS.len();
+            }
+            Position::Free => {
+                pos = next_pos;
+                map[pos.0 as usize][pos.1 as usize] =
+                    Position::Visited(HashSet::from_iter(vec![current_direction]));
+            }
+            Position::Visited(visits) => {
+                pos = next_pos;
+
+                if visits.contains(&current_direction) {
+                    return true;
+                }
+                let mut visits = visits.clone();
+                visits.insert(current_direction);
+                map[pos.0 as usize][pos.1 as usize] = Position::Visited(visits);
+            }
+        }
+    }
+    false
+}
+
+fn walk_the_map(map: &Vec<Vec<Position>>, mut pos: (i32, i32), compute_obstacles: bool) -> u32 {
+    let mut map = map.clone();
+    let mut current_direction = 0;
+    let mut visited = 1;
+    let mut obstacles = 0;
+    loop {
+        let direction = DIRECTIONS[current_direction];
+        let next_pos = (pos.0 + direction.0, pos.1 + direction.1);
+
+        if !is_in_map(&map, next_pos) {
+            break;
+        }
+
+        match &map[next_pos.0 as usize][next_pos.1 as usize] {
+            Position::Obstacle => {
+                current_direction = (current_direction + 1) % DIRECTIONS.len();
+            }
+            Position::Free => {
+                map[next_pos.0 as usize][next_pos.1 as usize] = Position::Obstacle;
+                if compute_obstacles && will_loop(&map, pos, current_direction) {
+                    obstacles += 1;
+                }
+                pos = next_pos;
+                map[pos.0 as usize][pos.1 as usize] =
+                    Position::Visited(HashSet::from_iter(vec![current_direction]));
+                visited += 1;
+            }
+            Position::Visited(visits) => {
+                pos = next_pos;
+                let mut visits = visits.clone();
+                visits.insert(current_direction);
+                map[pos.0 as usize][pos.1 as usize] = Position::Visited(visits);
+            }
+        }
+    }
+    
+    if compute_obstacles {
+        obstacles
+    } else {
+        visited
+    }
+}
+
+fn part_1(map: &Vec<Vec<Position>>, pos: (i32, i32)) -> u32 {
+    walk_the_map(&map, pos, false)
+}
+
+fn part_2(map: &Vec<Vec<Position>>, pos: (i32, i32)) -> u32 {
+    walk_the_map(&map, pos, true)
+}
+
+fn main() {
+    let args: Vec<String> = env::args().collect();
+    for arg in args.iter().skip(1) {
+        let input = read_input(&arg);
+        let (map, start) = parse_input(&input);
+        println!("[{}]", &arg);
+        println!("\t[Part 1] => Answer is '{}'.", part_1(&map, start));
+        println!("\t[Part 2] => Answer is '{}'.", part_2(&map, start));
+    }
+}