Solve day 18

input/18-0.in

@@ -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 +1,58 @@
+use std::collections::{HashMap, HashSet, VecDeque};
+
+static DIRECTIONS: [(isize, isize); 4] = [(0, -1), (1, 0), (0, 1), (-1, 0)];
+
+fn dijkstra(map: &HashSet<(usize, usize)>, size: usize) -> Option<usize> {
+    let mut queue = VecDeque::new();
+
+    queue.push_back((0usize, 0usize, 0usize));
+
+    let mut visited = HashSet::new();
+
+    while let Some((cx, cy, steps)) = queue.pop_front() {
+        if cx == size - 1 && cy == size - 1 {
+            return Some(steps);
+        }
+        if visited.insert((cx, cy)) {
+            for (nx, ny) in DIRECTIONS.iter().filter_map(|&(dx, dy)| {
+                Option::zip(
+                    cx.checked_add_signed(dx).filter(|&s| s < size),
+                    cy.checked_add_signed(dy).filter(|&s| s < size),
+                )
+            }) {
+                if !visited.contains(&(nx, ny)) && map.get(&(nx, ny)).is_none() {
+                    queue.push_back((nx, ny, steps + 1));
+                }
+            }
+        }
+    }
+
+    None
+}
+
+fn main() {
+    // let text = std::fs::read_to_string("input/18-0.in").unwrap();
+    // let size = 7;
+    // let first = 12;
+    let text = std::fs::read_to_string("input/18-1.in").unwrap();
+    let size = 71;
+    let first = 1024;
+
+    let mut iter = text.lines().map(|l| {
+        let (x, y) = l.split_once(',').unwrap();
+        (x.parse::<usize>().unwrap(), y.parse::<usize>().unwrap())
+    });
+
+    let mut map = iter.by_ref().take(first).collect::<HashSet<_>>();
+
+    let t = dijkstra(&map, size);
+    println!("{t:?}");
+
+    for d in iter {
+        map.insert(d);
+        if dijkstra(&map, size).is_none() {
+            println!("{d:?}");
+            break;
+        }
+    }
+}