day 23 solution

2023/data/examples/23.txt

@@ -0,0 +1,23 @@
+#.#####################
+#.......#########...###
+#######.#########.#.###
+###.....#.>.>.###.#.###
+###v#####.#v#.###.#.###
+###.>...#.#.#.....#...#
+###v###.#.#.#########.#
+###...#.#.#.......#...#
+#####.#.#.#######.#.###
+#.....#.#.#.......#...#
+#.#####.#.#.#########v#
+#.#...#...#...###...>.#
+#.#.#v#######v###.###v#
+#...#.>.#...>.>.#.###.#
+#####v#.#.###v#.#.###.#
+#.....#...#...#.#.#...#
+#.#########.###.#.#.###
+#...###...#...#...#.###
+###.###.#.###v#####v###
+#...#...#.#.>.>.#.>.###
+#.###.###.#.###.#.#v###
+#.....###...###...#...#
+#####################.#

2023/src/bin/23.rs

@@ -1,11 +1,199 @@
 advent_of_code::solution!(23);
 
-pub fn part_one(input: &str) -> Option<u32> {
+use std::collections::{HashMap, HashSet};
-    None
+
+struct Map {
+    m: [[char; 141]; 141],
+    width: usize,
+    height: usize,
 }
 
-pub fn part_two(input: &str) -> Option<u32> {
+type Coord = (usize, usize);
+
+fn parse(input: &str) -> Map {
+    let mut m = [[' '; 141]; 141];
+    let mut width = 0;
+    let mut height = 0;
+    for (x, line) in input.lines().enumerate() {
+        for (y, char) in line.chars().enumerate() {
+            m[x][y] = char;
+            width = y;
+        }
+        height = x;
+    }
+    Map { m, width, height }
+}
+
+fn find_path(map: &Map, start: Coord, path: &HashSet<Coord>) -> Option<usize> {
+    let mut p = path.clone();
+    let mut cur = start.clone();
+    loop {
+        p.insert(cur);
+        let mut next: Vec<Coord> = vec![];
+        let c = map.m[cur.0][cur.1];
+        if c == '>' {
+            next.push((cur.0, cur.1 + 1));
+        } else if c == '<' {
+            next.push((cur.0, cur.1 - 1));
+        } else if c == 'v' {
+            next.push((cur.0 + 1, cur.1));
+        } else {
+            if cur.1 > 0 {
+                let lcoord = (cur.0, cur.1 - 1);
+                let l = map.m[lcoord.0][lcoord.1];
+                if !p.contains(&lcoord) && l != '#' && l != '>' {
+                    next.push(lcoord);
+                }
+            }
+            if cur.1 < map.width - 1 {
+                let rcoord = (cur.0, cur.1 + 1);
+                let r = map.m[rcoord.0][rcoord.1];
+                if !p.contains(&rcoord) && r != '#' {
+                    next.push(rcoord);
+                }
+            }
+            if cur.0 > 0 {
+                let ucoord = (cur.0 - 1, cur.1);
+                let u = map.m[ucoord.0][ucoord.1];
+                if !p.contains(&ucoord) && u != '#' && u != 'v' {
+                    next.push(ucoord);
+                }
+            }
+            if cur.0 <= map.height - 1 {
+                let dcoord = (cur.0 + 1, cur.1);
+                let d = map.m[dcoord.0][dcoord.1];
+                if !p.contains(&dcoord) && d != '#' {
+                    next.push(dcoord);
+                }
+            }
+        }
+        if next.is_empty() {
+            return None;
+        } else if next.len() == 1 {
+            cur = next[0];
+        } else {
+            return next.iter().filter_map(|k| find_path(map, *k, &p)).max();
+        }
+        if cur.0 == map.height {
+            break;
+        }
+    }
+    Some(p.len())
+}
+
+pub fn part_one(input: &str) -> Option<usize> {
+    let map = parse(input);
+    find_path(&map, (0, 1), &HashSet::new())
+}
+
+type Graph = HashMap<Coord, HashMap<Coord, usize>>;
+
+fn to_graph(map: &Map, initial: Coord, start: Coord, r: &mut Graph) {
+    if !r.contains_key(&initial) {
+        r.insert(initial, HashMap::new());
+    }
+    let mut v: HashSet<Coord> = HashSet::new();
+    v.insert(initial);
+    let mut cur = start.clone();
+    let mut steps = 1;
+    if initial.0 == 0 && initial.1 == 1 {
+        steps -= 1;
+    }
+    loop {
+        let mut next: Vec<Coord> = vec![];
+        v.insert(cur);
+        if cur.1 > 0 {
+            let lcoord = (cur.0, cur.1 - 1);
+            let l = map.m[lcoord.0][lcoord.1];
+            if l != '#' {
+                next.push(lcoord);
+            }
+        }
+        if cur.1 <= map.width - 1 {
+            let rcoord = (cur.0, cur.1 + 1);
+            let r = map.m[rcoord.0][rcoord.1];
+            if r != '#' {
+                next.push(rcoord);
+            }
+        }
+        if cur.0 > 0 {
+            let ucoord = (cur.0 - 1, cur.1);
+            let u = map.m[ucoord.0][ucoord.1];
+            if u != '#' {
+                next.push(ucoord);
+            }
+        }
+        if cur.0 <= map.height - 1 {
+            let dcoord = (cur.0 + 1, cur.1);
+            let d = map.m[dcoord.0][dcoord.1];
+            if d != '#' {
+                next.push(dcoord);
+            }
+        }
+        if next.len() > 2 {
+            let parent = r.get_mut(&initial).unwrap();
+            if parent.contains_key(&cur) {
+                return;
+            } else {
+                parent.insert(cur, steps);
+                for x in next.iter() {
+                    to_graph(map, cur, *x, r);
+                }
+            }
+        } else {
+            if let Some(next_spot) = next.iter().find(|n| !v.contains(*n)) {
+                steps += 1;
+                cur = *next_spot;
+            } else {
+                let parent = r.get_mut(&initial).unwrap();
+                if !parent.contains_key(&cur) {
+                    parent.insert(cur, steps);
+                }
+                return;
+            }
+        }
+    }
+}
+
+fn dfs(
+    g: &Graph,
+    steps: usize,
+    cur: Coord,
+    dest: Coord,
+    visited: &mut HashSet<Coord>,
+) -> Option<usize> {
+    if cur == dest {
+        return Some(steps);
+    }
+    let neighbors = g.get(&cur).unwrap();
+    visited.insert(cur);
+    let m = neighbors
+        .iter()
+        .filter_map(|(n, dist)| {
+            if visited.contains(&n) {
                 None
+            } else if *n == dest {
+                Some(steps + dist)
+            } else {
+                dfs(g, steps + dist, *n, dest, visited)
+            }
+        })
+        .max();
+    visited.remove(&cur);
+    m
+}
+
+pub fn part_two(input: &str) -> Option<usize> {
+    let map = parse(input);
+    let mut g: Graph = HashMap::new();
+    to_graph(&map, (0, 1), (0, 1), &mut g);
+    dfs(
+        &g,
+        0,
+        (0, 1),
+        (map.height, map.width - 1),
+        &mut HashSet::new(),
+    )
 }
 
 #[cfg(test)]
@@ -15,12 +203,12 @@ mod tests {
     #[test]
     fn test_part_one() {
         let result = part_one(&advent_of_code::template::read_file("examples", DAY));
-        assert_eq!(result, None);
+        assert_eq!(result, Some(94));
     }
 
     #[test]
     fn test_part_two() {
         let result = part_two(&advent_of_code::template::read_file("examples", DAY));
-        assert_eq!(result, None);
+        assert_eq!(result, Some(154));
     }
 }