solution: 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 +1,94 @@
+use std::collections::VecDeque;
+
+use hashbrown::{HashMap, HashSet};
+use itertools::Itertools;
+
+use aoc::{
+    grid_vec::{Direction, Point},
+    pnt,
+};
+
+fn parse_input(input: &str) -> Vec<Point> {
+    input
+        .lines()
+        .map(|x| {
+            x.split(',')
+                .filter_map(|y| y.parse().ok())
+                .collect_tuple()
+                .unwrap()
+        })
+        .map(|x: (usize, usize)| Point { i: x.1, j: x.0 })
+        .collect_vec()
+}
+
+fn bfs(
+    visited: &mut HashMap<Point, usize>,
+    queue: &mut VecDeque<(Point, usize)>,
+    corruption: &HashSet<Point>,
+    end: Point,
+) -> Option<usize> {
+    visited.clear();
+    queue.clear();
+
+    queue.push_back((pnt!(0, 0), 0));
+
+    while let Some((p, l)) = queue.pop_front() {
+        if visited.contains_key(&p) {
+            continue;
+        }
+        visited.insert(p, l);
+
+        if p == end {
+            break;
+        }
+
+        for d in Direction::CROSS {
+            let n = p + d;
+
+            let in_bounds = n.bounded_by(&end);
+            let not_visited = !visited.contains_key(&n);
+            let not_corrupted = !corruption.contains(&n);
+
+            if in_bounds && not_visited && not_corrupted {
+                queue.push_back((n, l + 1));
+            }
+        }
+    }
+
+    visited.get(&end).copied()
+}
+
+pub fn part_one(input: &str) -> Option<usize> {
+    let falling_bytes = parse_input(input);
+
+    let mut visited = HashMap::new();
+    let mut queue = VecDeque::new();
+
+    let end = pnt!(70, 70);
+    let corruption = HashSet::from_iter(falling_bytes.iter().copied().take(1024));
+
+    bfs(&mut visited, &mut queue, &corruption, end)
+}
+
+pub fn part_two(input: &str) -> Option<String> {
+    let falling_bytes = parse_input(input);
+
+    let mut visited = HashMap::new();
+    let mut queue = VecDeque::new();
+
+    let end = pnt!(70, 70);
+    let mut corruption = HashSet::new();
+    let mut c = 0;
+
+    while bfs(&mut visited, &mut queue, &corruption, end).is_some() {
+        corruption.insert(falling_bytes[c]);
+        c += 1;
+    }
+
+    let fb = falling_bytes[c - 1];
+
+    Some(format!("{},{}", fb.j, fb.i))
+}
+
+aoc::solution!(18);
+