minor optimizations for p2. vec (with dfs) is faster than vecdeque

README.md

@@ -53,9 +53,9 @@ Solutions for [Advent of Code](https://adventofcode.com/) in [Rust](https://www.
 | [Day 16](./src/bin/16.rs) | `58.3µs` | `1.7ms` |
 | [Day 17](./src/bin/17.rs) | `1.6ms` | `3.7ms` |
 | [Day 18](./src/bin/18.rs) | `2.4µs` | `2.5µs` |
-| [Day 19](./src/bin/19.rs) | `165.3µs` | `642.5µs` |
+| [Day 19](./src/bin/19.rs) | `167.5µs` | `616.8µs` |
 
-**Total: 14.89ms**
+**Total: 14.86ms**
 <!--- benchmarking table --->
 
 ---

src/bin/19.rs

@@ -37,10 +37,10 @@ pub fn part_two(input: &str) -> Option<u64> {
 
     // BFS until we find accept nodes. Each path to an accept node results
     // in a volume of possible ratings. The union of those volumes is our answer.
-    let mut queue = VecDeque::new();
-    queue.push_back(("in", PartFilter::new(1, 4000)));
-    let mut accept_volumes = Vec::new();
-    while let Some((cur, filter)) = queue.pop_front() {
+    let mut stack = Vec::with_capacity(1000);
+    stack.push(("in", PartFilter::new(1, 4000)));
+    let mut accept_volumes = Vec::with_capacity(1000);
+    while let Some((cur, filter)) = stack.pop() {
         let workflow = &workflows[cur];
         let mut workflow_filter = Some(filter);
         for rule in &workflow.rules {
@@ -49,7 +49,7 @@ pub fn part_two(input: &str) -> Option<u64> {
             {
                 match rule.destination {
                     Destination::Accept => accept_volumes.push(new_filter),
-                    Destination::Next(d) => queue.push_back((d, new_filter)),
+                    Destination::Next(d) => stack.push((d, new_filter)),
                     Destination::Reject => {}
                 }
             }
@@ -62,7 +62,7 @@ pub fn part_two(input: &str) -> Option<u64> {
         if let Some(filter) = workflow_filter {
             match workflow.default_rule {
                 Destination::Accept => accept_volumes.push(filter),
-                Destination::Next(d) => queue.push_back((d, filter)),
+                Destination::Next(d) => stack.push((d, filter)),
                 Destination::Reject => {}
             }
         }