day 18

data/examples/18.txt

@@ -0,0 +1,25 @@
+5,4
+4,2
+4,5
+3,0
+2,1
+6,3
+2,4
+1,5
+0,6
+3,3
+2,6
+5,1
+1,2
+5,5
+2,5
+6,5
+1,4
+0,4
+6,4
+1,1
+6,1
+1,0
+0,5
+1,6
+2,0

src/bin/18.rs

@@ -0,0 +1,157 @@
+use std::collections::{HashMap, HashSet, VecDeque};
+
+advent_of_code::solution!(18);
+
+#[derive(Debug, Eq, Hash, PartialEq, Clone, Copy)]
+struct Pos(i32, i32);
+
+fn sum_pos(pos1: Pos, pos2: Pos) -> Pos {
+    Pos(pos1.0 + pos2.0, pos1.1 + pos2.1)
+}
+
+#[derive(Debug, Eq, Hash, PartialEq, Clone, Copy)]
+struct Move {
+    pos: Pos,
+    score: u32,
+}
+
+pub fn part_one(input: &str) -> Option<u32> {
+    let mut walls = HashSet::new();
+    let end = Pos(70, 70);
+    for (count, line) in input.lines().enumerate() {
+        if count >= 1024 {
+            break;
+        };
+
+        let (x, y) = line.split_once(",").unwrap();
+        walls.insert(Pos(x.parse().unwrap(), y.parse().unwrap()));
+    }
+    let mut min = 1000000;
+
+    let mut visited: HashMap<Pos, u32> = HashMap::new();
+    let mut queue = VecDeque::from_iter(vec![Move {
+        pos: Pos(0, 0),
+        score: 0,
+    }]);
+
+    while let Some(cand) = queue.pop_front() {
+        // handle end case
+        if cand.pos == end && cand.score < min {
+            min = cand.score;
+            continue;
+        }
+
+        // handle already seen but better
+        if let Some(cached) = visited.get(&(cand.pos)) {
+            if cached <= &cand.score {
+                continue;
+            }
+        };
+        *visited.entry(cand.pos).or_default() = cand.score;
+
+        let next_pos = vec![
+            (sum_pos(cand.pos, Pos(0, -1))),
+            (sum_pos(cand.pos, Pos(1, 0))),
+            (sum_pos(cand.pos, Pos(0, 1))),
+            (sum_pos(cand.pos, Pos(-1, 0))),
+        ];
+
+        for p in next_pos {
+            if walls.contains(&p) || p.0 > end.0 || p.0 < 0 || p.1 > end.1 || p.1 < 0 {
+                continue;
+            }
+
+            queue.push_back(Move {
+                pos: p,
+                score: cand.score + 1,
+            })
+        }
+    }
+    Some(min)
+}
+
+pub fn part_two(input: &str) -> Option<String> {
+    let mut walls = HashSet::new();
+    let mut future_walls = VecDeque::new();
+    let end = Pos(70, 70);
+    for (count, line) in input.lines().enumerate() {
+        let (x, y) = line.split_once(",").unwrap();
+        if count < 1024 {
+            walls.insert(Pos(x.parse().unwrap(), y.parse().unwrap()));
+        } else {
+            future_walls.push_back(Pos(x.parse().unwrap(), y.parse().unwrap()))
+        };
+    }
+
+    let mut res = String::new();
+    loop {
+        let mut min = 1000000;
+
+        let mut visited: HashMap<Pos, u32> = HashMap::new();
+        let mut queue = VecDeque::from_iter(vec![Move {
+            pos: Pos(0, 0),
+            score: 0,
+        }]);
+
+        while let Some(cand) = queue.pop_front() {
+            // handle end case
+            if cand.pos == end && cand.score < min {
+                min = cand.score;
+                continue;
+            }
+
+            // handle already seen but better
+            if let Some(cached) = visited.get(&(cand.pos)) {
+                if cached <= &cand.score {
+                    continue;
+                }
+            };
+            *visited.entry(cand.pos).or_default() = cand.score;
+
+            let next_pos = vec![
+                (sum_pos(cand.pos, Pos(0, -1))),
+                (sum_pos(cand.pos, Pos(1, 0))),
+                (sum_pos(cand.pos, Pos(0, 1))),
+                (sum_pos(cand.pos, Pos(-1, 0))),
+            ];
+
+            for p in next_pos {
+                if walls.contains(&p) || p.0 > end.0 || p.0 < 0 || p.1 > end.1 || p.1 < 0 {
+                    continue;
+                }
+
+                queue.push_back(Move {
+                    pos: p,
+                    score: cand.score + 1,
+                })
+            }
+        }
+
+        if min == 1000000 {
+            break;
+        } else if let Some(next_fallen) = future_walls.pop_front() {
+            res = format!("{},{}", next_fallen.0, next_fallen.1);
+            walls.insert(next_fallen);
+        } else {
+            break;
+        }
+    }
+    Some(res)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_part_one() {
+        let result = part_one(&advent_of_code::template::read_file("examples", DAY));
+        assert_eq!(result, Some(146));
+    }
+
+    #[test]
+    fn test_part_two() {
+        let result = part_two(&advent_of_code::template::read_file("examples", DAY));
+        assert_eq!(result, Some("".into()));
+    }
+}