From 8367b63c539a0153be124c32f14585c3ece6d96c Mon Sep 17 00:00:00 2001
From: Samuel Ortion <samuel@ortion.fr>
Date: Sun, 15 Dec 2024 11:18:27 +0100
Subject: [PATCH] 2024: day 10: part 1 and 2: rust

---
 2024/days/10/day10/Cargo.toml  |  6 +++
 2024/days/10/day10/src/main.rs | 96 ++++++++++++++++++++++++++++++++++
 2 files changed, 102 insertions(+)
 create mode 100644 2024/days/10/day10/Cargo.toml
 create mode 100644 2024/days/10/day10/src/main.rs

diff --git a/2024/days/10/day10/Cargo.toml b/2024/days/10/day10/Cargo.toml
new file mode 100644
index 0000000..3c916ef
--- /dev/null
+++ b/2024/days/10/day10/Cargo.toml
@@ -0,0 +1,6 @@
+[package]
+name = "day10"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
diff --git a/2024/days/10/day10/src/main.rs b/2024/days/10/day10/src/main.rs
new file mode 100644
index 0000000..d6daefe
--- /dev/null
+++ b/2024/days/10/day10/src/main.rs
@@ -0,0 +1,96 @@
+use std::collections::BTreeSet;
+
+fn parse_map(string: String) -> Vec<Vec<u32>> {
+    let mut map: Vec<Vec<u32>> = Vec::new();
+    for line in string.lines() {
+        let mut map_slice: Vec<u32> = Vec::new();
+        for letter in line.chars() {
+            let height: u32 = letter.to_digit(10).unwrap();
+            map_slice.push(height);
+        }
+        map.push(map_slice);
+    }
+    map
+}
+
+fn is_in_bound(x: isize, y: isize, width: usize, height: usize) -> bool {
+    x >= 0 && y >= 0 && y < height as isize && x < width as isize
+}
+
+fn trailhead_score(start_x: usize, start_y: usize, map: &Vec<Vec<u32>>) -> u32 {
+    let mut visited: BTreeSet<(usize, usize)> = BTreeSet::new();
+    let mut score: u32 = 0;
+    let mut queue: Vec<(usize, usize)> = Vec::new();
+    queue.push((start_x, start_y));
+    let moves: [(isize, isize); 4] = [(-1, 0), (0, -1), (1, 0), (0, 1)];
+    while !queue.is_empty() {
+        if let Some((x, y)) = queue.pop() {
+            if map[y][x] == 9 {
+                score += 1;
+            }
+            for (dx, dy) in moves {
+                let new_x = x as isize + dx;
+                let new_y = y as isize + dy;
+                if is_in_bound(new_x, new_y, map[0].len(), map.len())
+                    && map[new_y as usize][new_x as usize] > map[y][x]
+                    && map[new_y as usize][new_x as usize] - map[y][x] == 1
+                    && !visited.contains(&(new_x as usize, new_y as usize)) {
+                    queue.push((new_x as usize, new_y as usize));
+                }
+            }
+            visited.insert((x as usize, y as usize));
+        }
+    }
+    score
+}
+
+fn trailhead_paths(x: usize, y: usize, map: &Vec<Vec<u32>>) -> u32 {
+    if map[y][x] == 9 {
+        return 1;
+    } else {
+        let moves: [(isize, isize); 4] = [(-1, 0), (0, -1), (1, 0), (0, 1)];
+        let mut paths: u32 = 0;
+        for (dx, dy) in moves {
+            let new_x = x as isize + dx;
+            let new_y = y as isize + dy;
+            if is_in_bound(new_x, new_y, map[0].len(), map.len())
+                && map[new_y as usize][new_x as usize] > map[y][x]
+                && map[new_y as usize][new_x as usize] - map[y][x] == 1 {
+                let p = trailhead_paths(new_x as usize, new_y as usize, map);
+                paths += p;
+            }
+        }
+        return paths;
+    }
+}
+
+fn find_trailheads(map: &Vec<Vec<u32>>) -> Vec<(usize, usize)> {
+    let mut trailheads: Vec<(usize, usize)> = Vec::new();
+    for y in 0..map.len() {
+        for x in 0..map[y].len() {
+            if map[y][x] == 0 {
+                trailheads.push((x, y));
+            }
+        }
+    }
+    trailheads
+}
+
+fn main() -> std::io::Result<()> {
+    let input = std::io::read_to_string(std::io::stdin())?;
+    let map = parse_map(input);
+    let trailheads = find_trailheads(&map);
+    // Part 1.
+    let mut score = 0;
+    for (start_x, start_y) in &trailheads {
+        score += trailhead_score(*start_x, *start_y, &map);
+    }
+    println!("{}", score);
+    // Part 2.
+    let mut paths = 0;
+    for (start_x, start_y) in &trailheads {
+        paths += trailhead_paths(*start_x, *start_y, &map);
+    }
+    println!("{}", paths);
+    Ok(())
+}