Solve day 12

input/12

@@ -0,0 +1,41 @@
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input/12-test

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

src/bin/12.rs

@@ -0,0 +1,165 @@
+use aoc2022::*;
+use itertools::Itertools;
+
+const INPUT: &str = include_str!("../../input/12");
+
+fn main() {
+    let mut hill = Hill::from_input();
+    hill.mark_dijkstra();
+    solved_level_1(hill.level1());
+    solved_level_2(hill.level2());
+}
+
+#[derive(PartialEq, Eq, Hash, Clone, Copy, Debug)]
+struct Position {
+    x: usize,
+    y: usize,
+}
+
+impl Position {
+    fn new(x: usize, y: usize) -> Self {
+        Self { x, y }
+    }
+}
+
+#[derive(Debug, Clone)]
+struct Node {
+    chr: char,
+    visited: bool,
+    distance: usize,
+    position: Position,
+}
+
+#[derive(Debug)]
+struct Hill {
+    nodes: Vec<Vec<Node>>,
+    start: Position,
+    end: Position,
+}
+
+impl Hill {
+    fn level1(&self) -> usize {
+        self.get(self.start).distance
+    }
+
+    fn level2(&self) -> usize {
+        self.nodes
+            .iter()
+            .flat_map(|row| row.iter())
+            .filter(|n| n.chr == 'a')
+            .map(|n| n.distance)
+            .min()
+            .unwrap()
+    }
+
+    // Mark each node with its distance to the end.
+    fn mark_dijkstra(&mut self) {
+        self.get_mut(self.end).distance = 0;
+
+        loop {
+            // Find unvisited node with minimal distance
+            let subject = self
+                .nodes
+                .iter()
+                .flat_map(|row| row.iter())
+                .filter(|n| !n.visited)
+                .filter(|n| n.distance < usize::MAX)
+                .min_by_key(|n| n.distance)
+                .cloned();
+            // If there is no such node then we are done.
+            let Some(subject) = subject else { return };
+
+            self.get_mut(subject.position).visited = true;
+
+            // Find and update neighbors
+            let mut neighbors = Vec::with_capacity(4);
+            if subject.position.x > 0 {
+                neighbors.push(Position::new(subject.position.x - 1, subject.position.y));
+            }
+            if subject.position.x < self.nodes[0].len() - 1 {
+                neighbors.push(Position::new(subject.position.x + 1, subject.position.y));
+            }
+            if subject.position.y > 0 {
+                neighbors.push(Position::new(subject.position.x, subject.position.y - 1));
+            }
+            if subject.position.y < self.nodes.len() - 1 {
+                neighbors.push(Position::new(subject.position.x, subject.position.y + 1));
+            }
+            let neighbors = neighbors
+                .into_iter()
+                .filter(|&n| !self.get(n).visited)
+                .filter(|&n| climbable(self.get(n).chr, subject.chr))
+                .collect_vec();
+
+            let new_distance = subject.distance + 1;
+            for neighbor in neighbors {
+                let mut neighbor = self.get_mut(neighbor);
+                neighbor.distance = neighbor.distance.min(new_distance);
+            }
+        }
+    }
+
+    fn get_mut(&mut self, p: Position) -> &mut Node {
+        &mut self.nodes[p.y][p.x]
+    }
+
+    fn get(&self, p: Position) -> &Node {
+        &self.nodes[p.y][p.x]
+    }
+
+    fn from_input() -> Self {
+        let mut start = None;
+        let mut end = None;
+
+        let nodes = INPUT
+            .lines()
+            .enumerate()
+            .map(|(y, line)| {
+                line.chars()
+                    .enumerate()
+                    .map(|(x, c)| {
+                        let position = Position::new(x, y);
+
+                        if c == 'S' {
+                            start = Some(position);
+                        } else if c == 'E' {
+                            end = Some(position);
+                        }
+
+                        Node {
+                            chr: c,
+                            visited: false,
+                            distance: usize::MAX,
+                            position,
+                        }
+                    })
+                    .collect_vec()
+            })
+            .collect_vec();
+
+        Self {
+            nodes,
+            start: start.unwrap(),
+            end: end.unwrap(),
+        }
+    }
+}
+
+fn climbable(from: char, to: char) -> bool {
+    let from = convert(from);
+    let to = convert(to);
+    if to < from {
+        return true;
+    }
+
+    from.abs_diff(to) <= 1
+}
+
+fn convert(c: char) -> u32 {
+    let c = match c {
+        'S' => 'a',
+        'E' => 'z',
+        c => c,
+    };
+    c as u32
+}