From fff824749461ec0b0badc0027d31f3a9fc61e6e3 Mon Sep 17 00:00:00 2001
From: Kevin Caffrey <kcaffrey@gmail.com>
Date: Thu, 14 Dec 2023 21:51:16 -0500
Subject: [PATCH] somehow this is faster and I don't understand fully why. I
 guess avoiding a branch that wrecks branch prediction?

---
 README.md     |  4 ++--
 src/bin/14.rs | 18 ++++++------------
 2 files changed, 8 insertions(+), 14 deletions(-)

diff --git a/README.md b/README.md
index db5f86b..d3e47d2 100644
--- a/README.md
+++ b/README.md
@@ -43,9 +43,9 @@ Solutions for [Advent of Code](https://adventofcode.com/) in [Rust](https://www.
 | [Day 11](./src/bin/11.rs) | `16.3µs` | `15.7µs` |
 | [Day 12](./src/bin/12.rs) | `137.9µs` | `618.3µs` |
 | [Day 13](./src/bin/13.rs) | `12.3µs` | `15.9µs` |
-| [Day 14](./src/bin/14.rs) | `24.4µs` | `10.7ms` |
+| [Day 14](./src/bin/14.rs) | `26.7µs` | `5.5ms` |
 
-**Total: 13.11ms**
+**Total: 7.91ms**
 <!--- benchmarking table --->
 
 ---
diff --git a/src/bin/14.rs b/src/bin/14.rs
index 12d6a0a..02b654e 100644
--- a/src/bin/14.rs
+++ b/src/bin/14.rs
@@ -61,7 +61,6 @@ struct Platform {
     height: u8,
     round_rocks: Vec<Coordinate>,
     distance_to_cubed_rocks: Vec<Vec<CachedDistance>>,
-    rock_stacks: Vec<Vec<RockStack>>,
     iteration: u16,
 }
 
@@ -101,11 +100,9 @@ impl Platform {
                 };
             }
         }
-        let rock_stacks = vec![vec![RockStack::default(); grid[0].len()]; grid.len()];
         Self {
             round_rocks,
             distance_to_cubed_rocks,
-            rock_stacks,
             iteration: 0,
             width,
             height,
@@ -127,25 +124,22 @@ impl Platform {
 
     fn tilt(&mut self, dir: Direction) {
         self.iteration += 1;
+        let mut stacks = vec![vec![0; self.width as usize]; self.height as usize];
         for rock in &mut self.round_rocks {
             let distance =
                 self.distance_to_cubed_rocks[rock.row as usize][rock.col as usize].get(dir);
             let cubed_rock = rock
                 .move_in_dir(dir, distance)
                 .limit_to(self.height - 1, self.width - 1);
-            let stack = &mut self.rock_stacks[cubed_rock.row as usize][cubed_rock.col as usize];
-            if stack.iteration != self.iteration {
-                stack.iteration = self.iteration;
-                stack.count = 0;
-            }
-            if stack.count > distance - 1 {
-                let total_move_distance = stack.count - distance + 1;
+            let stack = &mut stacks[cubed_rock.row as usize][cubed_rock.col as usize];
+            if *stack > distance - 1 {
+                let total_move_distance = *stack - distance + 1;
                 *rock = rock.move_in_dir(dir.rev(), total_move_distance);
             } else {
-                let total_move_distance = distance - 1 - stack.count;
+                let total_move_distance = distance - 1 - *stack;
                 *rock = rock.move_in_dir(dir, total_move_distance);
             }
-            stack.count += 1;
+            *stack += 1;
         }
     }