Day 23, part 1

src/bin/d23p1.rs

@@ -0,0 +1,19 @@
+use aoc22::{
+    day23::{self, empty_ground},
+    util,
+};
+
+const N_ROUNDS: usize = 10;
+
+pub fn main() {
+    let mut elves = day23::parse_map(&util::parse_input());
+
+    for i in 0..N_ROUNDS {
+        let elves_too_close = day23::do_round(&mut elves, i);
+        if !elves_too_close {
+            break;
+        }
+    }
+
+    println!("Elves cover {} empty tiles", empty_ground(&elves));
+}

src/day23.rs

@@ -0,0 +1,112 @@
+use std::collections::{HashMap, HashSet};
+
+use itertools::Itertools;
+
+use crate::util::{self, SignedCoord};
+
+pub fn parse_map(input: &str) -> HashSet<SignedCoord> {
+    let mut result = HashSet::new();
+    for (y, row) in input.lines().enumerate() {
+        for (x, c) in row.chars().enumerate() {
+            if c == '#' {
+                result.insert((y as isize, x as isize));
+            }
+        }
+    }
+    result
+}
+
+const NUM_DIRS: usize = 4;
+
+pub fn do_round(elves: &mut HashSet<SignedCoord>, it: usize) -> bool {
+    let mut proposals: HashMap<SignedCoord, Vec<SignedCoord>> = HashMap::new();
+
+    let mut elves_too_close = false;
+    for elf in elves.iter() {
+        if noone_adjacent(elves, elf) {
+            continue;
+        }
+        elves_too_close = true;
+        for offset in 0..NUM_DIRS {
+            let dir = (it + offset) % NUM_DIRS;
+            if let Some(new_loc) = propose(elves, elf, dir) {
+                proposals.entry(new_loc).or_insert_with(Vec::new).push(*elf);
+                break;
+            }
+        }
+    }
+
+    for (target, interested) in proposals {
+        if interested.len() == 1 {
+            elves.remove(&interested[0]);
+            elves.insert(target);
+        }
+    }
+
+    elves_too_close
+}
+
+fn noone_adjacent(elves: &HashSet<SignedCoord>, elf: &SignedCoord) -> bool {
+    !(elves.contains(&(elf.0, elf.1 + 1))
+        || elves.contains(&(elf.0, elf.1 - 1))
+        || elves.contains(&(elf.0 + 1, elf.1))
+        || elves.contains(&(elf.0 + 1, elf.1 + 1))
+        || elves.contains(&(elf.0 + 1, elf.1 - 1))
+        || elves.contains(&(elf.0 - 1, elf.1))
+        || elves.contains(&(elf.0 - 1, elf.1 + 1))
+        || elves.contains(&(elf.0 - 1, elf.1 - 1)))
+}
+
+fn propose(elves: &HashSet<SignedCoord>, elf: &SignedCoord, dir: usize) -> Option<SignedCoord> {
+    let (moved, other) = match dir {
+        0 => (
+            (elf.0 - 1, elf.1),
+            ((elf.0 - 1, elf.1 - 1), (elf.0 - 1, elf.1 + 1)),
+        ), // N
+        1 => (
+            (elf.0 + 1, elf.1),
+            ((elf.0 + 1, elf.1 - 1), (elf.0 + 1, elf.1 + 1)),
+        ), // S
+        2 => (
+            (elf.0, elf.1 - 1),
+            ((elf.0 - 1, elf.1 - 1), (elf.0 + 1, elf.1 - 1)),
+        ), // E
+        3 => (
+            (elf.0, elf.1 + 1),
+            ((elf.0 - 1, elf.1 + 1), (elf.0 + 1, elf.1 + 1)),
+        ), // W
+        _ => panic!("Unknown direction {}", dir),
+    };
+    if elves.contains(&moved) || elves.contains(&other.0) || elves.contains(&other.1) {
+        None
+    } else {
+        Some(moved)
+    }
+}
+
+pub fn print_map(elves: &HashSet<SignedCoord>) {
+    let (y_min, y_max) = util::minmax_unwrap(&elves.iter().map(|c| c.0).minmax());
+    let (x_min, x_max) = util::minmax_unwrap(&elves.iter().map(|c| c.1).minmax());
+
+    println!("({}, {})", y_min, x_min);
+    for y in y_min..(y_max + 1) {
+        for x in x_min..(x_max + 1) {
+            if elves.contains(&(y, x)) {
+                print!("#");
+            } else {
+                print!(".");
+            }
+        }
+        print!("\n");
+    }
+    print!("\n");
+}
+
+pub fn empty_ground(elves: &HashSet<SignedCoord>) -> usize {
+    let (y_min, y_max) = util::minmax_unwrap(&elves.iter().map(|c| c.0).minmax());
+    let (x_min, x_max) = util::minmax_unwrap(&elves.iter().map(|c| c.1).minmax());
+    let y_dim = (y_max + 1 - y_min) as usize;
+    let x_dim = (x_max + 1 - x_min) as usize;
+
+    y_dim * x_dim - elves.len()
+}

src/lib.rs

@@ -13,6 +13,7 @@ pub mod day2;
 pub mod day20;
 pub mod day21;
 pub mod day22;
+pub mod day23;
 pub mod day3;
 pub mod day4;
 pub mod day5;

src/util.rs

@@ -3,6 +3,8 @@ use std::env;
 use std::fs;
 use std::hash::Hash;
 
+use itertools::MinMaxResult;
+
 pub fn parse_input() -> String {
     let args: Vec<String> = env::args().collect();
     let input_path = args
@@ -153,3 +155,11 @@ impl Dir {
         Self::from_usize((d + 3) % 4).unwrap()
     }
 }
+
+pub fn minmax_unwrap<T: Clone>(mm: &MinMaxResult<T>) -> (T, T) {
+    match mm {
+        MinMaxResult::NoElements => panic!("No elements"),
+        MinMaxResult::OneElement(a) => (a.clone(), a.clone()),
+        MinMaxResult::MinMax(a, b) => (a.clone(), b.clone()),
+    }
+}