preallocate a little memory for the DFS stack

README.md

@@ -59,9 +59,9 @@ Solutions for [Advent of Code](https://adventofcode.com/) in [Rust](https://www.
 | [Day 19](./src/bin/19.rs) | `83.9µs` | `90.9µs` |
 | [Day 20](./src/bin/20.rs) | `323.9µs` | `1.2ms` |
 | [Day 21](./src/bin/21.rs) | `64.1µs` | `494.7µs` |
-| [Day 22](./src/bin/22.rs) | `85.3µs` | `205.8µs` |
+| [Day 22](./src/bin/22.rs) | `82.4µs` | `202.8µs` |
 
-**Total: 16.63ms**
+**Total: 16.62ms**
 <!--- benchmarking table --->
 
 ---

src/bin/22.rs

@@ -24,7 +24,7 @@ pub fn part_two(input: &str) -> Option<u32> {
             .map(|brick| {
                 let mut fall_count = 0;
                 let mut visited = vec![false; tower.bricks.len()];
-                let mut stack = Vec::new();
+                let mut stack = Vec::with_capacity(16);
                 visited[brick] = true;
                 stack.push(brick);
                 while let Some(cur) = stack.pop() {