From 15de4852fa7f129d095aa0b2b9c0bddd38be6153 Mon Sep 17 00:00:00 2001
From: Louis Vallat <contact@louis-vallat.dev>
Date: Wed, 11 Dec 2024 23:59:45 +0100
Subject: [PATCH] feat: added day 10 part 1 and 2

Signed-off-by: Louis Vallat <contact@louis-vallat.dev>
---
 .gitea/workflows/build_and_run.yml |  2 +-
 day10/Cargo.toml                   |  6 +++
 day10/src/main.rs                  | 80 ++++++++++++++++++++++++++++++
 3 files changed, 87 insertions(+), 1 deletion(-)
 create mode 100644 day10/Cargo.toml
 create mode 100644 day10/src/main.rs

diff --git a/.gitea/workflows/build_and_run.yml b/.gitea/workflows/build_and_run.yml
index 97ca62c..2f2b049 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]
+        day_number: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
     runs-on: rust-bookworm
     steps:
       - name: Check out repository code
diff --git a/day10/Cargo.toml b/day10/Cargo.toml
new file mode 100644
index 0000000..3c916ef
--- /dev/null
+++ b/day10/Cargo.toml
@@ -0,0 +1,6 @@
+[package]
+name = "day10"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
diff --git a/day10/src/main.rs b/day10/src/main.rs
new file mode 100644
index 0000000..5d8f7bb
--- /dev/null
+++ b/day10/src/main.rs
@@ -0,0 +1,80 @@
+use std::collections::HashSet;
+use std::{env, fs};
+
+fn read_input(path: &str) -> String {
+    fs::read_to_string(path).expect("Cannot read file.")
+}
+
+fn parse_input(input: &str) -> (Vec<Vec<usize>>, HashSet<(usize, usize)>) {
+    let mut map = Vec::new();
+    let mut trail_heads = HashSet::new();
+    for (row, line) in input.lines().filter(|line| !line.is_empty()).enumerate() {
+        map.push(Vec::new());
+        for (col, char) in line.chars().enumerate() {
+            map.last_mut()
+                .unwrap()
+                .push(char.to_digit(10).unwrap() as usize);
+            if char == '0' {
+                trail_heads.insert((row, col));
+            }
+        }
+    }
+    (map, trail_heads)
+}
+
+fn trails_count(
+    map: &Vec<Vec<usize>>,
+    current: (usize, usize),
+    nines: &mut HashSet<(usize, usize)>,
+) -> usize {
+    if map[current.0][current.1] == 9 {
+        nines.insert(current);
+        return 1;
+    }
+
+    let mut sum = 0;
+    for direction in [(0, 1), (1, 0), (0, -1), (-1, 0)] {
+        let target = (
+            current.0 as i32 + direction.0,
+            current.1 as i32 + direction.1,
+        );
+        if (0..map.len() as i32).contains(&target.0)
+            && (0..map[target.0 as usize].len() as i32).contains(&target.1)
+        {
+            let target = (target.0 as usize, target.1 as usize);
+            if map[target.0][target.1] == map[current.0][current.1] + 1 {
+                sum += trails_count(map, target, nines);
+            }
+        }
+    }
+    sum
+}
+
+fn part_1(map: &Vec<Vec<usize>>, trail_heads: &HashSet<(usize, usize)>) -> usize {
+    trail_heads
+        .iter()
+        .map(|(row, col)| {
+            let mut nines = HashSet::new();
+            trails_count(map, (*row, *col), &mut nines);
+            nines.len()
+        })
+        .sum()
+}
+
+fn part_2(map: &Vec<Vec<usize>>, trail_heads: &HashSet<(usize, usize)>) -> usize {
+    trail_heads
+        .iter()
+        .map(|(row, col)| trails_count(map, (*row, *col), &mut HashSet::new()))
+        .sum()
+}
+
+fn main() {
+    let args: Vec<String> = env::args().collect();
+    for arg in args.iter().skip(1) {
+        let input = read_input(&arg);
+        let (map, trail_heads) = parse_input(&input);
+        println!("[{}]", &arg);
+        println!("\t[Part 1] => Answer is '{}'.", part_1(&map, &trail_heads));
+        println!("\t[Part 2] => Answer is '{}'.", part_2(&map, &trail_heads));
+    }
+}