From 2aefc33bc221190463d926ca97b284bffc9eb72d Mon Sep 17 00:00:00 2001
From: Jeremy Kaplan <jdkaplan@metagram.net>
Date: Tue, 13 Dec 2022 22:46:43 -0800
Subject: [PATCH] =?UTF-8?q?Fix=20mutually-correcting=20bugs=20=F0=9F=98=85?=
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---
 2022/src/bin/day14.rs | 66 ++++++++++++++++++-------------------------
 1 file changed, 27 insertions(+), 39 deletions(-)

diff --git a/2022/src/bin/day14.rs b/2022/src/bin/day14.rs
index 097a084..b668307 100644
--- a/2022/src/bin/day14.rs
+++ b/2022/src/bin/day14.rs
@@ -3,28 +3,25 @@ use std::collections::HashSet;
 const INPUT: &str = include_str!("../../input/day14.txt");
 
 fn main() {
-    println!("{}", part1(INPUT));
-    println!("{}", part2(INPUT));
+    let paths = aoc::lines(INPUT).map(Path::parse).collect();
+    let wall = Wall::build(paths);
+
+    println!("{}", part1(wall.clone()));
+    println!("{}", part2(wall));
 }
 
-fn part1(input: &str) -> usize {
-    let paths = aoc::lines(input).map(Path::parse).collect();
-    let mut wall = Wall::build(paths);
-
+fn part1(mut wall: Wall) -> usize {
     while wall.add_sand_1().is_some() {}
 
     wall.render();
     wall.sand.len()
 }
 
-fn part2(input: &str) -> usize {
-    let paths = aoc::lines(input).map(Path::parse).collect();
-    let mut wall = Wall::build(paths);
-
+fn part2(mut wall: Wall) -> usize {
     while let Some(_pos) = wall.add_sand_2() {}
 
     wall.render();
-    wall.sand.len() + 1 // for the sand source
+    wall.sand.len()
 }
 
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
@@ -96,6 +93,7 @@ impl Segment {
     }
 }
 
+#[derive(Debug, Clone)]
 struct Wall {
     rocks: HashSet<Point>,
     sand: HashSet<Point>,
@@ -120,7 +118,7 @@ impl Wall {
             }
         }
 
-        let y_floor = y_abyss;
+        let y_floor = y_abyss + 2;
 
         Self {
             rocks,
@@ -178,7 +176,10 @@ impl Point {
 
 impl Wall {
     fn filled(&self, p: &Point) -> bool {
-        p == &Wall::SAND_SOURCE || self.rocks.contains(p) || self.sand.contains(p)
+        p == &Wall::SAND_SOURCE
+            || self.rocks.contains(p)
+            || self.sand.contains(p)
+            || p.y >= self.y_floor
     }
 
     fn empty(&self, p: &Point) -> bool {
@@ -186,25 +187,7 @@ impl Wall {
     }
 
     fn add_sand_1(&mut self) -> Option<Point> {
-        let mut pos = Wall::SAND_SOURCE;
-
-        'tick: while pos.y <= self.y_abyss {
-            let candidates = vec![
-                pos.mv(0, 1),  // down
-                pos.mv(-1, 1), // down-left
-                pos.mv(1, 1),  // down-right
-            ];
-
-            for next in candidates {
-                if self.empty(&next) {
-                    pos = next;
-                    continue 'tick;
-                }
-            }
-
-            // Stuck!
-            break 'tick;
-        }
+        let pos = self.drop_sand(self.y_abyss);
 
         if pos.y < self.y_abyss {
             self.sand.insert(pos);
@@ -215,9 +198,19 @@ impl Wall {
     }
 
     fn add_sand_2(&mut self) -> Option<Point> {
+        let pos = self.drop_sand(self.y_floor);
+
+        if self.sand.insert(pos) {
+            Some(pos)
+        } else {
+            None
+        }
+    }
+
+    fn drop_sand(&self, y_max: i32) -> Point {
         let mut pos = Wall::SAND_SOURCE;
 
-        'tick: while pos.y <= self.y_floor {
+        'tick: while pos.y <= y_max {
             let candidates = vec![
                 pos.mv(0, 1),  // down
                 pos.mv(-1, 1), // down-left
@@ -235,12 +228,7 @@ impl Wall {
             break 'tick;
         }
 
-        if pos != Wall::SAND_SOURCE {
-            self.sand.insert(pos);
-            Some(pos)
-        } else {
-            None
-        }
+        pos
     }
 }