day(12): add initial solution

Signed-off-by: Matej Focko <mfocko@redhat.com>

samples/day12.txt

@@ -0,0 +1,5 @@
+Sabqponm
+abcryxxl
+accszExk
+acctuvwj
+abdefghi

src/bin/day12.rs

@@ -0,0 +1,146 @@
+use std::{
+    collections::{BTreeSet, VecDeque},
+};
+
+use aoc_2022::*;
+
+use itertools::Itertools;
+
+type Input = Vec<Vec<char>>;
+type Output = usize;
+
+type Position = Vector2D<isize>;
+
+fn find(map: &[Vec<char>], expected: char) -> Option<Position> {
+    for (y, row) in map.iter().enumerate() {
+        for (x, &c) in row.iter().enumerate() {
+            if c == expected {
+                return Some(Position::new(x as isize, y as isize));
+            }
+        }
+    }
+
+    None
+}
+
+fn find_start(map: &[Vec<char>]) -> Position {
+    if let Some(pos) = find(map, 'S') {
+        pos
+    } else {
+        panic!("haven't found start")
+    }
+}
+
+fn find_target(map: &[Vec<char>]) -> Position {
+    if let Some(pos) = find(map, 'E') {
+        pos
+    } else {
+        panic!("haven't found target")
+    }
+}
+
+#[derive(Debug)]
+struct Vertex {
+    position: Position,
+    distance: usize,
+}
+
+impl Vertex {
+    fn new(position: Position, distance: usize) -> Self {
+        Self { position, distance }
+    }
+}
+
+fn get_elevation(c: char) -> i32 {
+    match c {
+        'S' => get_elevation('a'),
+        'E' => get_elevation('z'),
+        _ => c as i32 - 'a' as i32,
+    }
+}
+
+struct Day12;
+impl Solution<Input, Output> for Day12 {
+    fn parse_input<P: AsRef<Path>>(pathname: P) -> Input {
+        file_to_lines(pathname)
+            .into_iter()
+            .map(|line| line.chars().collect_vec())
+            .collect_vec()
+    }
+
+    fn part_1(input: &Input) -> Output {
+        let start = find_start(input);
+        let target = find_target(input);
+
+        let mut visited: BTreeSet<Position> = BTreeSet::new();
+        let mut queue: VecDeque<Vertex> = VecDeque::new();
+        visited.insert(start);
+        queue.push_back(Vertex::new(start, 0));
+
+        while let Some(v) = queue.pop_front() {
+            // debug!("Taking {:?} from queue", v);
+
+            for (dx, dy) in [(0, 1), (1, 0), (0, -1), (-1, 0)] {
+                let d = Position::new(dx, dy);
+                let neighbour = v.position + d;
+
+                let current = get_elevation(*index(input, &v.position));
+                if in_range(input, &neighbour)
+                    && (get_elevation(*index(input, &neighbour)) <= current + 1)
+                    && !visited.contains(&neighbour)
+                {
+                    if neighbour == target {
+                        // debug!("Found target at distance {}", v.distance + 1);
+                        return v.distance + 1;
+                    }
+
+                    visited.insert(neighbour);
+                    queue.push_back(Vertex::new(neighbour, v.distance + 1));
+                }
+            }
+        }
+
+        panic!("haven't found path to target")
+    }
+
+    fn part_2(input: &Input) -> Output {
+        let start = find_target(input);
+
+        let mut visited: BTreeSet<Position> = BTreeSet::new();
+        let mut queue: VecDeque<Vertex> = VecDeque::new();
+        visited.insert(start);
+        queue.push_back(Vertex::new(start, 0));
+
+        while let Some(v) = queue.pop_front() {
+            // debug!("Taking {:?} from queue at elevation {}", v, get_elevation(*index(input, &v.position)));
+
+            for (dx, dy) in [(0, 1), (1, 0), (0, -1), (-1, 0)] {
+                let d = Position::new(dx, dy);
+                let neighbour = v.position + d;
+
+                let current = get_elevation(*index(input, &v.position));
+                if in_range(input, &neighbour)
+                    && (current - get_elevation(*index(input, &neighbour))) <= 1
+                    && !visited.contains(&neighbour)
+                {
+                    if get_elevation(*index(input, &neighbour)) == 0 {
+                        // debug!("Found target at distance {}", v.distance + 1);
+                        return v.distance + 1;
+                    }
+
+                    visited.insert(neighbour);
+                    queue.push_back(Vertex::new(neighbour, v.distance + 1));
+                }
+            }
+        }
+
+        panic!("haven't found path to target")
+    }
+}
+
+fn main() -> Result<()> {
+    // Day12::run("sample")
+    Day12::main()
+}
+
+test_sample!(day_12, Day12, 31, 29);