Day 23

res/23/input.txt

@@ -0,0 +1,75 @@
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res/23/test-input.txt

@@ -0,0 +1,7 @@
+....#..
+..###.#
+#...#.#
+.#...##
+#.###..
+##.#.##
+.#..#..

src/days/d23.rs

@@ -0,0 +1,171 @@
+use std::{collections::HashMap, fs};
+
+const OFFSET: usize = 500;
+
+pub fn solve() {
+    let path = "res/23/input.txt";
+
+    let contents = fs::read_to_string(path).expect("I/O error, wrong path?");
+
+    let read_grid: Vec<Vec<bool>> = contents
+        .lines()
+        .filter(|&line| line != "")
+        .map(|line| {
+            line.chars()
+                .map(|c| match c {
+                    '.' => false,
+                    '#' => true,
+                    _ => std::unreachable!(),
+                })
+                .collect::<Vec<bool>>()
+        })
+        .collect();
+
+    let mut grid = vec![vec![false; read_grid[0].len() + 2 * OFFSET]; read_grid.len() + 2 * OFFSET];
+    for (y, line) in read_grid.iter().enumerate() {
+        for (x, val) in line.iter().enumerate() {
+            if *val {
+                grid[y + OFFSET][x + OFFSET] = true
+            }
+        }
+    }
+
+    // run 10 rounds
+    for i in 0..10 {
+        run_round(&mut grid, i);
+    }
+
+    let mut min_y = grid.len();
+    let mut max_y = 0usize;
+    let mut min_x = grid[0].len();
+    let mut max_x = 0usize;
+    let mut elf_counter = 0;
+    for (y, line) in grid.iter().enumerate() {
+        for (x, val) in line.iter().enumerate() {
+            if *val {
+                min_y = min_y.min(y);
+                max_y = max_y.max(y);
+                min_x = min_x.min(x);
+                max_x = max_x.max(x);
+                elf_counter += 1;
+            }
+        }
+    }
+
+    let res = (max_y - min_y + 1) * (max_x - min_x + 1) - elf_counter;
+    println!("Result 1: {res}");
+
+    // task 2
+    let mut round = 10;
+    while run_round(&mut grid, round) != 0 {
+        round += 1;
+    }
+    println!("Result 2: {}", round + 1)
+}
+
+fn new_pos(y: usize, x: usize, round: i32, grid: &Vec<Vec<bool>>) -> Option<(usize, usize)> {
+    if !grid[y][x] {
+        return None;
+    }
+
+    let mut elf_adjacent = false;
+    for yi in -1..=1 {
+        for xi in -1..=1 {
+            if (xi != 0 || yi != 0) && grid[(y as i64 + yi) as usize][(x as i64 + xi) as usize] {
+                elf_adjacent = true;
+            }
+        }
+    }
+    if !elf_adjacent {
+        return None;
+    }
+
+    let north: Vec<(i64, i64)> = vec![(-1, -1), (-1, 0), (-1, 1)];
+    let south: Vec<(i64, i64)> = vec![(1, -1), (1, 0), (1, 1)];
+    let west: Vec<(i64, i64)> = vec![(-1, -1), (0, -1), (1, -1)];
+    let east: Vec<(i64, i64)> = vec![(-1, 1), (0, 1), (1, 1)];
+
+    let order = match round % 4 {
+        0 => {
+            // north
+            vec![north, south, west, east]
+        }
+        1 => {
+            // south
+            vec![south, west, east, north]
+        }
+        2 => {
+            // west
+            vec![west, east, north, south]
+        }
+        3 => {
+            // east
+            vec![east, north, south, west]
+        }
+        _ => std::unreachable!(),
+    };
+
+    for dir in order {
+        if grid[(y as i64 + dir[0].0) as usize][(x as i64 + dir[0].1) as usize] {
+            continue;
+        }
+        if grid[(y as i64 + dir[1].0) as usize][(x as i64 + dir[1].1) as usize] {
+            continue;
+        }
+        if grid[(y as i64 + dir[2].0) as usize][(x as i64 + dir[2].1) as usize] {
+            continue;
+        }
+        return Some((
+            (y as i64 + dir[1].0) as usize,
+            (x as i64 + dir[1].1) as usize,
+        ));
+    }
+
+    return None;
+}
+
+// Runs a round, returns how many elves moved
+fn run_round(grid: &mut Vec<Vec<bool>>, round: i32) -> usize {
+    let mut changes_map = HashMap::<(usize, usize), Vec<(usize, usize)>>::new();
+
+    for (y, line) in grid.iter().enumerate() {
+        for (x, _) in line.iter().enumerate() {
+            match new_pos(y, x, round, &grid) {
+                Some((new_y, new_x)) => {
+                    if changes_map.contains_key(&(new_y, new_x)) {
+                        changes_map.get_mut(&(new_y, new_x)).unwrap().push((y, x));
+                    } else {
+                        changes_map.insert((new_y, new_x), vec![(y, x)]);
+                    }
+                }
+                None => {}
+            }
+        }
+    }
+
+    let mut elf_move_counter = 0usize;
+
+    for (pos, old_pos_vec) in changes_map {
+        // if only one elf wants to go to position
+        if old_pos_vec.len() == 1 {
+            grid[old_pos_vec[0].0][old_pos_vec[0].1] = false;
+            grid[pos.0][pos.1] = true;
+            elf_move_counter += 1;
+        }
+    }
+
+    return elf_move_counter;
+}
+
+fn _print_grid(grid: &Vec<Vec<bool>>) {
+    for y in grid.iter() {
+        for x in y.iter() {
+            match *x {
+                true => print!("#"),
+                false => print!("."),
+            }
+        }
+        println!()
+    }
+    println!();
+}

src/main.rs

@@ -1,7 +1,7 @@
 pub mod days;
 
 fn main() {
-    days::d21::solve()
+    days::d23::solve()
     //_all_days()
 }