From e74071df2c0da296f8cc18cc59dabaf8f46cfba1 Mon Sep 17 00:00:00 2001
From: Jeremy Kaplan <jdkaplan@metagram.net>
Date: Fri, 16 Dec 2022 23:29:07 -0800
Subject: [PATCH] 2022 Day 17 Part 1

---
 2022/src/bin/day17.rs | 263 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 263 insertions(+)
 create mode 100644 2022/src/bin/day17.rs

diff --git a/2022/src/bin/day17.rs b/2022/src/bin/day17.rs
new file mode 100644
index 0000000..3878777
--- /dev/null
+++ b/2022/src/bin/day17.rs
@@ -0,0 +1,263 @@
+use std::{convert::TryInto, fmt::Display, str::FromStr};
+
+use serde::{
+    de::{value, IntoDeserializer},
+    Deserialize,
+};
+
+// const INPUT: (&str, usize) = (include_str!("../../input/day17-ex.txt"), 10);
+const INPUT: (&str, usize) = (include_str!("../../input/day17.txt"), 2022);
+
+fn main() {
+    let (text, rock_count) = INPUT;
+    let jets = parse_input(text);
+    println!("{}", part1(jets, rock_count));
+}
+
+#[derive(Debug, Copy, Clone, PartialEq, Eq, Hash, Deserialize)]
+enum Direction {
+    #[serde(rename = "<")]
+    Left,
+    #[serde(rename = ">")]
+    Right,
+}
+
+impl FromStr for Direction {
+    type Err = value::Error;
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        Self::deserialize(s.into_deserializer())
+    }
+}
+
+fn parse_input(text: &str) -> Vec<Direction> {
+    text.trim()
+        .chars()
+        .map(|c| Direction::from_str(&c.to_string()).unwrap())
+        .collect()
+}
+
+#[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
+enum Piece {
+    Dash,
+    Plus,
+    Corner,
+    Line,
+    Square,
+}
+
+impl Piece {
+    fn generator() -> impl Iterator<Item = Self> {
+        use Piece::*;
+        [Dash, Plus, Corner, Line, Square].into_iter().cycle()
+    }
+
+    fn new_rows(&self) -> Vec<Row> {
+        #[rustfmt::skip]
+        let rows: Vec<&str> = match self {
+            Piece::Dash => vec![
+                "..####.",
+            ],
+            Piece::Plus => vec![
+                "...#...",
+                "..###..",
+                "...#...",
+            ],
+            Piece::Corner => vec![
+                "....#..",
+                "....#..",
+                "..###..",
+            ],
+            Piece::Line => vec![
+                "..#....",
+                "..#....",
+                "..#....",
+                "..#....",
+            ],
+            Piece::Square => vec![
+                ".......",
+                "..##...",
+                "..##...",
+            ],
+        };
+
+        rows.iter()
+            .rev() // Bottom-up!
+            .map(|row| {
+                let bools: Vec<bool> = row.chars().map(|c| c == '#').collect();
+                TryInto::<Row>::try_into(bools).unwrap()
+            })
+            .collect()
+    }
+}
+
+// Stored bottom-up!
+#[derive(Debug, Clone)]
+struct Block(Vec<Row>);
+
+impl Block {
+    fn new(p: Piece) -> Self {
+        Self(p.new_rows())
+    }
+
+    fn push(&self, dir: Direction) -> Option<Self> {
+        let rows = Row::push_all(&self.0, dir);
+        rows.map(Self)
+    }
+}
+
+#[derive(Debug, Copy, Clone)]
+struct Row([bool; 7]);
+
+impl Row {
+    const EMPTY: Self = Self([false; 7]);
+
+    fn is_empty(&self) -> bool {
+        self.0.iter().all(|&v| !v)
+    }
+
+    fn intersects(&self, other: &Self) -> bool {
+        self.0.iter().zip(other.0.iter()).any(|(&t, &p)| t && p)
+    }
+
+    fn merge(&self, other: &Self) -> Self {
+        let pairs = self.0.iter().zip(other.0.iter());
+        let a: Vec<bool> = pairs
+            .map(|(&t, &p)| {
+                if t && p {
+                    panic!("merging piece that collides with tower");
+                }
+                t || p
+            })
+            .collect();
+        a.into()
+    }
+
+    fn push(&self, dir: Direction) -> Result<Self, ()> {
+        match dir {
+            Direction::Left => {
+                // Touching left edge, can't move.
+                if self.0[0] {
+                    Err(())
+                } else {
+                    let mut a = self.0;
+                    a.rotate_left(1);
+                    Ok(Self(a))
+                }
+            }
+            Direction::Right => {
+                // Touching right edge, can't move.
+                if self.0[6] {
+                    Err(())
+                } else {
+                    let mut a = self.0;
+                    a.rotate_right(1);
+                    Ok(Self(a))
+                }
+            }
+        }
+    }
+
+    fn push_all(rs: &[Self], dir: Direction) -> Option<Vec<Self>> {
+        let pushed: Result<Vec<Self>, ()> = rs.iter().cloned().map(|r| r.push(dir)).collect();
+        pushed.ok()
+    }
+}
+
+impl From<Vec<bool>> for Row {
+    fn from(v: Vec<bool>) -> Self {
+        Self(v.try_into().unwrap())
+    }
+}
+
+#[derive(Debug, Clone)]
+struct Tower {
+    grid: Vec<Row>,
+}
+
+impl Tower {
+    fn new() -> Self {
+        Self { grid: vec![] }
+    }
+
+    fn height(&self) -> usize {
+        let empty_rows = self.grid.iter().rev().take_while(|r| r.is_empty()).count();
+        self.grid.len() - empty_rows
+    }
+
+    fn spawn(&mut self, piece: Piece, jets: &mut impl Iterator<Item = Direction>) {
+        self.grid.extend([Row::EMPTY; 4]);
+
+        let mut block = Block::new(piece);
+        let mut y = self.height() + 3;
+
+        loop {
+            // Push!
+            let dir = jets.next().unwrap();
+            if let Some(new_block) = block.push(dir) {
+                if self.can_place(y, &new_block) {
+                    block = new_block;
+                }
+            };
+
+            // Fall!
+            let Some(new_y) = y.checked_sub(1) else {
+                break;
+            };
+            if self.can_place(new_y, &block) {
+                y = new_y;
+            } else {
+                break;
+            }
+        }
+
+        self.place_at(y, block);
+
+        self.grid.truncate(self.height());
+    }
+
+    fn can_place(&self, y: usize, block: &Block) -> bool {
+        let mut window = self.grid[y..].iter().zip(&block.0);
+        !window.any(|(tower, piece)| tower.intersects(piece))
+    }
+
+    fn place_at(&mut self, y: usize, block: Block) {
+        for (yy, p) in (y..).zip(block.0) {
+            let tower = self.grid[yy];
+            self.grid[yy] = tower.merge(&p);
+        }
+    }
+}
+
+fn part1(jets: Vec<Direction>, rock_count: usize) -> usize {
+    let pieces = Piece::generator().take(rock_count);
+    let mut jets = jets.into_iter().cycle();
+
+    let mut tower = Tower::new();
+
+    for piece in pieces {
+        tower.spawn(piece, &mut jets);
+        // tower.render();
+    }
+
+    tower.height()
+}
+
+impl Tower {
+    fn render(&self) {
+        for (i, row) in self.grid.iter().enumerate().rev() {
+            println!("{} {}", i, row);
+        }
+        println!("  -------");
+    }
+}
+
+impl Display for Row {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        for occupied in self.0 {
+            let c = if occupied { '#' } else { '.' };
+            write!(f, "{}", c)?
+        }
+        Ok(())
+    }
+}