[2021] Day 15: Part a

Author: connorslade

Cargo.lock

@@ -5,6 +5,8 @@ edition = "2021"
 
 [dependencies]
 common = { path = "../common" }
+aoc_lib = { path = "../aoc_lib" }
+
 hashbrown = "0.13.1"
 indoc = "2.0.4"
 nd_vec = "0.4.0"

aoc_2021/Cargo.toml

@@ -0,0 +1,85 @@
+use std::collections::VecDeque;
+
+use aoc_lib::{direction::Direction, matrix::Matrix};
+use common::{Answer, Solution};
+use hashbrown::HashMap;
+use nd_vec::vector;
+
+type Pos = nd_vec::Vec2<usize>;
+
+pub struct Day15;
+
+impl Solution for Day15 {
+    fn name(&self) -> &'static str {
+        "Chiton"
+    }
+
+    fn part_a(&self, input: &str) -> Answer {
+        let matrix = Matrix::new_chars(input, |chr| chr.to_digit(10).unwrap() as u8);
+
+        let mut out = usize::MAX;
+        let mut visited = HashMap::new();
+        let mut queue = VecDeque::new();
+        queue.push_back((vector!(0, 0), 0));
+
+        while let Some((pos, cost)) = queue.pop_front() {
+            if pos == matrix.size - vector!(1, 1) {
+                out = out.min(cost);
+                continue;
+            }
+
+            visited.insert(pos, cost);
+            for dir in Direction::ALL {
+                if let Some((next, new_cost)) = dir
+                    .try_advance(pos)
+                    .and_then(|x| Some((x, cost + *matrix.get(x)? as usize)))
+                {
+                    if let Some(prev) = visited.get(&next) {
+                        if *prev <= new_cost {
+                            continue;
+                        }
+                    }
+
+                    queue.push_back((next, new_cost));
+                }
+            }
+        }
+
+        out.into()
+    }
+
+    fn part_b(&self, input: &str) -> Answer {
+        Answer::Unimplemented
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use common::Solution;
+    use indoc::indoc;
+
+    use super::Day15;
+
+    const CASE: &str = indoc! {"
+        1163751742
+        1381373672
+        2136511328
+        3694931569
+        7463417111
+        1319128137
+        1359912421
+        3125421639
+        1293138521
+        2311944581
+    "};
+
+    #[test]
+    fn part_a() {
+        assert_eq!(Day15.part_a(CASE), 40.into());
+    }
+
+    #[test]
+    fn part_b() {
+        assert_eq!(Day15.part_b(CASE), ().into());
+    }
+}

aoc_2021/src/day_15.rs

@@ -14,6 +14,7 @@ mod day_11;
 mod day_12;
 mod day_13;
 mod day_14;
+mod day_15;
 // [import_marker]
 
 pub const ALL: &[&dyn Solution] = &[
@@ -31,6 +32,6 @@ pub const ALL: &[&dyn Solution] = &[
     &day_12::Day12,
     &day_13::Day13,
     &day_14::Day14,
-    &day_12::Day12,
+    &day_15::Day15,
     // [list_marker]
 ];