From b5538fd3aacc1b9e6ed5e1d5b993d6e9330fdddc Mon Sep 17 00:00:00 2001
From: Louis Vallat <contact@louis-vallat.dev>
Date: Sat, 14 Dec 2024 15:44:01 +0100
Subject: [PATCH] feat: added day 12 part 1 and 2

Signed-off-by: Louis Vallat <contact@louis-vallat.dev>
---
 .gitea/workflows/build_and_run.yml |   2 +-
 day12/Cargo.toml                   |   6 ++
 day12/src/main.rs                  | 111 +++++++++++++++++++++++++++++
 3 files changed, 118 insertions(+), 1 deletion(-)
 create mode 100644 day12/Cargo.toml
 create mode 100644 day12/src/main.rs

diff --git a/.gitea/workflows/build_and_run.yml b/.gitea/workflows/build_and_run.yml
index db09ccd..43e3f1c 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, 6, 7, 8, 9, 10, 11]
+        day_number: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12]
     runs-on: rust-bookworm
     steps:
       - name: Check out repository code
diff --git a/day12/Cargo.toml b/day12/Cargo.toml
new file mode 100644
index 0000000..be558ad
--- /dev/null
+++ b/day12/Cargo.toml
@@ -0,0 +1,6 @@
+[package]
+name = "day12"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
diff --git a/day12/src/main.rs b/day12/src/main.rs
new file mode 100644
index 0000000..0c1572a
--- /dev/null
+++ b/day12/src/main.rs
@@ -0,0 +1,111 @@
+use std::collections::HashSet;
+use std::{env, fs};
+
+const DIRECTIONS: [(i32, i32); 4] = [(0, 1), (1, 0), (0, -1), (-1, 0)];
+
+fn read_input(path: &str) -> String {
+    fs::read_to_string(path).expect("Cannot read file.")
+}
+
+fn parse_input(input: &str) -> Vec<Vec<char>> {
+    input
+        .lines()
+        .filter(|line| !line.is_empty())
+        .map(|line| line.chars().collect())
+        .collect()
+}
+
+fn walk_garden(
+    map: &Vec<Vec<char>>,
+    current: (i32, i32),
+    visited: &mut HashSet<(i32, i32)>,
+    borders: &mut HashSet<(i32, i32, usize)>,
+) -> (usize, usize) {
+    visited.insert(current);
+    let mut perimeter = 0;
+    let mut area = 1;
+    for (i, direction) in DIRECTIONS.iter().enumerate() {
+        let target = (current.0 + direction.0, current.1 + direction.1);
+        if (0..map.len() as i32).contains(&target.0)
+            && (0..map[target.0 as usize].len() as i32).contains(&target.1)
+        {
+            if map[target.0 as usize][target.1 as usize]
+                == map[current.0 as usize][current.1 as usize]
+            {
+                if visited.contains(&target) {
+                    continue;
+                }
+                let result = walk_garden(map, target, visited, borders);
+                area += result.0;
+                perimeter += result.1;
+            } else {
+                borders.insert((current.0, current.1, i));
+                perimeter += 1;
+            }
+        } else {
+            borders.insert((current.0, current.1, i));
+            perimeter += 1;
+        }
+    }
+
+    (area, perimeter)
+}
+
+fn count_sides(borders: &mut HashSet<(i32, i32, usize)>) -> usize {
+    let mut sides = 0;
+    while let Some((row, col, direction)) = borders.iter().last().cloned() {
+        sides += 1;
+        borders.remove(&(row, col, direction));
+        for target_dir in [
+            (direction + 1) % DIRECTIONS.len(),
+            (direction + DIRECTIONS.len() - 1) % DIRECTIONS.len(),
+        ] {
+            let mut target = (row, col);
+            loop {
+                target.0 += DIRECTIONS[target_dir].0;
+                target.1 += DIRECTIONS[target_dir].1;
+                if !borders.remove(&(target.0, target.1, direction)) {
+                    break;
+                }
+            }
+        }
+    }
+
+    sides
+}
+
+fn compute_map_data(map: &Vec<Vec<char>>) -> Vec<(usize, usize, usize)> {
+    let mut visited = HashSet::new();
+    let mut data = Vec::new();
+    for (row, line) in map.iter().enumerate() {
+        for (col, _) in line.iter().enumerate() {
+            if visited.contains(&(row as i32, col as i32)) {
+                continue;
+            }
+            let mut borders = HashSet::new();
+            let (area, perimeter) =
+                walk_garden(map, (row as i32, col as i32), &mut visited, &mut borders);
+            data.push((area, perimeter, count_sides(&mut borders)));
+        }
+    }
+
+    data
+}
+
+fn main() {
+    let args: Vec<String> = env::args().collect();
+    for arg in args.iter().skip(1) {
+        let input = read_input(&arg);
+        let map = parse_input(&input);
+        let map_data = compute_map_data(&map);
+        println!("[{}]", &arg);
+        println!(
+            "\t[Part 1] => Answer is '{}'.",
+            map_data.iter().map(|data| data.0 * data.1).sum::<usize>()
+        );
+        println!(
+            "\t[Part 2] => Answer is '{}'.",
+            map_data.iter().map(|data| data.0 * data.2).sum::<usize>()
+        );
+    }
+}