Day 12, puzzle 2

src/bin/d12p1.rs

@@ -0,0 +1,9 @@
+use aoc22::{day12, util};
+
+pub fn main() {
+    let heightmap = day12::parse_heightmap(&util::parse_input());
+
+    let dist = day12::path_steps(&heightmap, false).expect("No path found!?");
+
+    println!("Distance to target is {}", dist);
+}

src/bin/d12p2.rs

@@ -0,0 +1,9 @@
+use aoc22::{day12, util};
+
+pub fn main() {
+    let heightmap = day12::parse_heightmap(&util::parse_input());
+
+    let dist = day12::path_steps(&heightmap, true).expect("No path found!?");
+
+    println!("Distance to target is {}", dist);
+}

src/day12.rs

@@ -0,0 +1,95 @@
+use std::collections::VecDeque;
+
+use itertools::Itertools;
+
+pub type Coord = (usize, usize);
+
+#[derive(Debug)]
+pub struct Heightmap {
+    pub map: Vec<Vec<usize>>,
+    pub rows: usize,
+    pub cols: usize,
+    pub start: Coord,
+    pub target: Coord,
+}
+
+pub fn parse_heightmap(input: &String) -> Heightmap {
+    let mut start = (usize::MAX, usize::MAX);
+    let mut target = (usize::MAX, usize::MAX);
+    let map = input
+        .lines()
+        .enumerate()
+        .map(|(row, l)| {
+            l.as_bytes()
+                .iter()
+                .enumerate()
+                .map(|(col, c)| {
+                    if *c == ('S' as u8) {
+                        start = (row, col);
+                        0
+                    } else if *c == ('E' as u8) {
+                        target = (row, col);
+                        25
+                    } else {
+                        (c - ('a' as u8)) as usize
+                    }
+                })
+                .collect_vec()
+        })
+        .collect_vec();
+
+    assert_ne!(start.0, usize::MAX);
+    assert_ne!(target.0, usize::MAX);
+
+    let rows = map.len();
+    let cols;
+    if let itertools::MinMaxResult::MinMax(min, max) = map.iter().map(|r| r.len()).minmax() {
+        cols = min;
+        assert_eq!(min, max);
+    } else {
+        panic!("<2 rows?");
+    }
+
+    Heightmap {
+        map,
+        cols,
+        rows,
+        start,
+        target,
+    }
+}
+
+pub fn path_steps(map: &Heightmap, any_a: bool) -> Option<usize> {
+    let mut dist = vec![vec![usize::MAX; map.cols]; map.rows];
+    dist[map.target.0][map.target.1] = 0;
+    let mut next = VecDeque::new();
+    next.push_back(map.target);
+
+    let moves: Vec<(isize, isize)> = vec![(1, 0), (-1, 0), (0, 1), (0, -1)];
+    while let Some(coord) = next.pop_front() {
+        let curr_height = map.map[coord.0][coord.1];
+        let curr_dist = dist[coord.0][coord.1];
+        if curr_height == 0 && (any_a || coord == map.start) {
+            return Some(curr_dist);
+        }
+
+        for move_ in &moves {
+            let y = (coord.0 as isize) + move_.0;
+            if y < 0 || y >= map.rows as isize {
+                continue;
+            }
+            let x = (coord.1 as isize) + move_.1;
+            if x < 0 || x >= map.cols as isize {
+                continue;
+            }
+            let y = y as usize;
+            let x = x as usize;
+            if map.map[y][x] + 1 >= curr_height && dist[y][x] > curr_dist + 1 {
+                dist[y][x] = curr_dist + 1;
+                next.push_back((y, x));
+            }
+        }
+    }
+
+    None
+}

src/lib.rs

@@ -1,6 +1,7 @@
 pub mod day1;
 pub mod day10;
 pub mod day11;
+pub mod day12;
 pub mod day2;
 pub mod day3;
 pub mod day4;