d21 with weird offset

res/21/example

@@ -0,0 +1,11 @@
+...........
+.....###.#.
+.###.##..#.
+..#.#...#..
+....#.#....
+.##..S####.
+.##..#...#.
+.......##..
+.##.#.####.
+.##..##.##.
+...........

res/21/input

@@ -0,0 +1,131 @@
+...................................................................................................................................
+......#...........#................#......................................#.....#......#..##.#.......#....#.#........#...##...#....
+...........#.................##...#...##......#............#...........##..#....................#.................#......#....#..#.
+.....#.........#.....#.#.....###........###........#..........................##..##.......#.......#.....#...............#.......#.
+....#..#......#......................#......#...............................#...........#........................#.............#...
+.......#.....................#.............#......#...............#....................#............#.#.........#..#...............
+.#.#.....#....#...................##......#..#..................#............................................#...............#.....
+.....#....#...#....##...#......#.............#......##........#................#................#................#...............#.
+.......#...................#..........#......................................#.........................##.........#..#.#..#........
+....#..........#.........#....#......##...........##.................#................#...#............#...#..##....#...........#..
+...#..........###............#.............#........................##..................#...##..................##......#...#......
+.......#.......#.#..#.......#.......##..........#.........#..............................##.....#..#..........#.....#......#.......
+..#.........#.....#..#..#..#..................#.........................#......................#.#..#...#..........#.....#....##.#.
+..................................#.....#................#........#..........................#........#.....#...............#....#.
+..........#..........#.#.................#.#.........................................#.......#..........#..##...#......#...........
+.........#........#...........#...#.#....#.................##..#....................#..........#....#.#....##........#.......#.....
+....#........#....................##..#......................#......#.........................#..#............................#....
+...#.#...#...#......................#..#..........................#...#.#...............#......#.#........#....#..........#.....#..
+..............#.....#.#......#........#...#..........#..#.#..#.........................#.....#..#......#.......#......#.......#....
+.......................#.....#.....#................................##...#..#...#...........#..#..........#..#.#...#.........#...#.
+.........#........#......#..#................................#.##.........#...#.................##......#.........#.##...#...#.....
+.#.#.........##....#..........#..##.....................#..##...#..#..#...#.......#...........................#....................
+.#.#......#..#..............##.#...#.#.............#.........#..............#.....#...............#..........................#...#.
+.....##.....#.....##..#...#..#..#......................................#......#.............#.............#.....#......#........#..
+......................#........#................#.......#..........#.............##............#..........#....#............#......
+.....#..............................#.......##......#..#....#..............#.....................................#.....#.........#.
+....................##...........#................#.#.....#.............#......#..##...#....................#................#.#...
+.................................#...........#.....#..#..#..............#..##.........#..............#......#................#.....
+............##.................................#..#...##.#........#...................................#...........#.#........#...#.
+...#.......#.#........#......#...........#....#..#.......#....#........#.#.#.............##.......#.................#..............
+...###............#......................##..##.........................#.........#......#..............#..#............#..........
+..#.......#...##...#..#.......#.......#...#...........................................#...................#........##....#..#......
+..#..................#.....#...........#.................#.#.#...........#..................#............#.......#.................
+...##..#.............#.....#.....................#................#..........................#.............##...............#......
+............#....#....#...#............#....#...........#.#.................#....#..................................#..............
+...#.....#.............#...........................#.....##..........#...............#....#...............#........................
+......#.....##.........#..........##..#...............#....#..#.#.#.....#.............#.###..............#..#......................
+....................#...#...............#....................#...............#.#.#..##.............................#...............
+...................#...#...........#...#.#...#...........#..............#............#..#......#............#.............#......#.
+...#................#.................#.....#..........#........#.#........#...................#..#...........#.##........#......#.
+....................#..........#....................#....#...#.....................#.......#.................#......#........#.....
+...#.........#...................#.......##...###......#..#.......#.#..................#............#...........#....#...........#.
+......#..#.#...#.#...............#.......................#.........#.......##................#...................#.###.............
+...............#..............................................#.....#....#...#..#...#.....#......#.....#...........................
+.......#.......#..........#.#.#..#.....#...#......#.................#........#...#..#.#.......#....................................
+...........#..#.....................#.........................#...#.#.....#..........#....##.....#.................................
+.......#.#.#.#..........#...#.##.##..#....................#.#.#..............#...................#....##...........................
+.........................#.#.#...................#......#......#.............#.....#..............#......###..............#.#......
+......#...............#...........#...................##..............#.##..#.#.#.#.#......#.....#.##.......#............#.#....##.
+.....#....#.............#..##........###...#.......#.....#....#.......###....................#..#.#............................#...
+.#........................#.....#......#.#.....................#......#.#...........#..#.....#.#.#..........#..............#...#...
+.....##...#.........#.#.#.#...................#..#..#.#..#...#..#.....#.#.....#.........##.........................................
+.................#.#...............#...............#...........#...........#.....#..........#...#.............................#....
+.......................##...........#..........#...............#..#......................................#...#................#..#.
+......#......................#..##.#........#.............#.....#..#....................#......#.........#.....#...#...........#.#.
+.....................#.................#....##..#....#....##..#..............#..............#.....#...............#................
+.#.................##.....#.#....#.....................#.............#....#......#...................#.#.##....................#...
+.##..........##....#.##......#..#.................#...#..##........#....#..#.......#..............#.......#........................
+......................#...........###.#.....##.............##........#..................#..............................#........#..
+..#........................#...................#.#.#...#........#........#....#.....#.....#........................#...............
+.#...........................#........#.....................#.....##.#..#.....#......#....#...#............##......................
+............#...#..#..........#..............#...#...#..#..........#.........#...............#....#.#......#.#...#.................
+..............................#..##...............#.....#....#.........................#....#...#....#.....#....#..................
+..................#.#.........................#.......#........#.......#..##....#...#....#..................................#......
+..........................#..#...#....................................#......#...#...#..#...#....#.............#.#.................
+.................................................................S.................................................................
+..............#...#...#.....##....#..................#....#........##..#.....#.#...#.#..............#.................##...........
+.........##.........#............##.............................#.#...#.#.......#..........####....#...........#...........#.......
+.........#...............................#...............#........................#......#..#......#.............##................
+.............#..............................#...#.................#..........###.#.#.#.........#........#..........................
+.#........#..#...........##...........#.#..........................#.........#....#.............#.............##...................
+..#..........#..........................#...#..#..#.##...#..............#.....#...#............##........#.#.......#............#..
+.................#.........#.......#.......#............#.#.................##...#.##.....................#.....#..................
+.#.##..........#...#...................#...#.....##.....#...............#..#.........#..............#.................#............
+.....#.......#..##....#..........#........#.#.....#.........#...............##......#.#....#.....#.................#...............
+......#.......#.#...#....................#...............#.........#....#..#.#..........##.....#...#........................#......
+.#.................#.................#.#....................#..............#.................#......#.......#.....#................
+.#..#................................#......#..........#..............#.#.##.......................#...............................
+..#.#............#.#......#...............#.#....#...#.#..#.......#...#.....#.......#........#.#...........#...#............##.....
+.......#..........#....#....................#................##...........#......#..#...#....#...#......................#...#.#....
+.........##........#........#......#.......#........#..#................#..#.............#..................#.#..........#.........
+......#....#.................................#..#.#....#..............#........#.....#.##........#..........#.............#....#...
+.............#........#.........#...##.....#.....#................##..........#.......#....#.......................................
+..........................#.....#..#......#....#....#..##...#.......................#..............#.......#..........#..#......#..
+...#.......................#....#.......#......#..................#................#...##........##.#............................#.
+....#....................#.####..........#......#.....#......#....#.#.#................#...#..............#.............#.....#....
+..........#..#...#..............##..#..#..#..........#.......#.##........##..............#.....#......#............#...#...........
+..........................#..#..............#..#....#..#..............#.#...#..........#.....#..#.#................................
+.......#.......#...............#.........#..#.#...#.....................#.....#......................#..............#.#..#.........
+........#.....#.............#....................#.#........#.................#.....#...#..........#............#...............#..
+.............#....##.........#.#................#....#.........#...#.......................#.....#.#..................#......#.....
+...............#.....#.............#.....#.......#.......#......#.#..#.....#...#...#.......#................#...#................#.
+...................#..#...........#..###....................#......#........#......#...........................#......#.......#....
+..#.....#.##......#................#.................#.................##....................#.#...........#....#.#...#........#...
+....#......#.#..#........#..............#.......#.........#.................#.............#.#...#...........#.#................#...
+..#....#.#.......#...#.................#......#....#................#.......................#...#.........##..........#.........#..
+..............#...............................#.##..............................#.......#..#...#...................#...#........#..
+.#..#....#......#.....#...#............#..............................#..............#....................#..##..............#..##.
+.......##............#..#............######............#................#..........#.#...#...#................#....................
+...#..................##....................#.......#.#....##...................##..#....#..#..........#.....#.....................
+...#.....#..#..#.#.......................#......................#...........#......###...#.............#........................#..
+.....#.............#..........#......................#....#............#.##....#.......#.............#..........#........##........
+........#...#.#..................#........#.#......#........#.....##...#...#....#...#......................................#.......
+...............#............#..#.......................##.#.....#...#.#........#..................#......#.........................
+.............##..#.......#.#.....#............#............#..........##.......#.....##...............................#...#........
+.#..##...............#..............#...........#..#..#...##.......#..#.......................#.......##.....................#.#...
+.....................###........#..#.....................#........#...#.##...................#....##.........#.........#...........
+...#.....#...............#....#..###.......................................#..................#....................................
+...#.#.#.....#..#.........#.....#...##.............#................#......#.....#........................#....#..............#....
+...........#......#..##.......#......#..................#.....##..................#........#.......#......#...#...#..#...#.........
+.........#.#.........#......#............................#.....#............#.................#..........#..............#.......#..
+............#.........#.#....#.......#...................................#..............##.##..............#....#...............#..
+.............#.....##.........#.........##...............#...............#.............................###........#.....#.#........
+......##..........#....#.#.#..........##.#.#................#...#....##.......................#.......#...#.#........#.#..#........
+....#....#............#.#......#..#.........#.............#.#..........................#.......#..............#..#..#.....#........
+...................#...........#....#...#..#..#.......#..#...#.#........................#.................#.............#..........
+.........#..#...#......#......#......#.................#...........#...................#........#.......#......#.#.......#.......#.
+..#..#......#.....................#...........................#.....##................#.............................#..............
+..#.#.......#........................#.......#..........................#................#.....#...#.........#.#......#............
+...............................#....................................#.......................##....#......#.#.........#.#.........#.
+.#.....................#......#..........#......#..............#...............##............#...#.##...#......##...#.#.#..........
+...............#.#......#..................#......................................................#........................#.#.....
+...#...#..#...............##...#...#.....#...#....................#..#..........#.....##......................................#....
+.#..#...#........................#....#...##......#...........#.......................#...##......#.......#................#.......
+....#...........#.............#.....#..#..#.....#.................................#........#.#..............#......................
+....#....#........#..#.#..............#................................................#..............#................#.........#.
+.....#..........#.......#..................#................................................#..............##...#..................
+................#...............#..........#............##.........................#........#.#...............#...##...............
+........#..................#..#.....#.#.........#.....#.#.#..................#.......#.#......#....#.........#..#.........#...#....
+..#...........##...............#...........#..#...#...#.#..................##......#.....#.......#........#..#...#......#........#.
+...................................................................................................................................

src/days/d21.rs

@@ -1,16 +1,98 @@
-use std::fs;
+use std::{fs, collections::{HashMap, VecDeque}};
+
+use num::Integer;
 
 pub fn solve() {
-    let path = "res/21/example";
+    let path = "res/21/input";
 
-    let mut _contents = fs::read_to_string(path).expect("I/O error, wrong path?");
+    let contents = fs::read_to_string(path).expect("I/O error, wrong path?");
     //let contents = BufReader::new(fs::File::open(path).expect("I/O error, wrong path?"));
+    let grid: Vec<Vec<char>> = contents.lines().map(|line| line.chars().collect::<Vec<_>>()).collect();
 
-    let result: usize = 0;
+    let s = find_char_location(&grid, 'S').unwrap();
+
+    const STEPS1: usize = 64;
+    let map = floodfill(&grid, s, STEPS1);
+
+    let result: usize = map.iter().filter(|(_, dist)| dist.is_even()).count();
 
     println!("Result 1: {result}");
 
-    let result: usize = 0;
+        
+    const STEPS2: usize = 26501365;
+    let x_len = grid.len();
+    let y_len = grid[0].len();
+    let steps_in_first = (x_len-1)/2;
+    let copies_per_dir = (STEPS2-steps_in_first)/x_len;
+
+    let pos_per_odd = floodfill(&grid, (0, 0), x_len+y_len).iter().filter(|(_, dist)| dist.is_odd()).count();
+    let pos_per_even = floodfill(&grid, (0, 0), x_len+y_len).iter().filter(|(_, dist)| dist.is_even()).count();
+
+    let cross = copies_per_dir * 2 * (pos_per_odd + pos_per_even) + pos_per_odd;
+    let triangles = 4 * (1..copies_per_dir).map(|i| if i.is_odd() {i*pos_per_odd} else {i*pos_per_even}).sum::<usize>();
+
+    let lefttop_odd = floodfill(&grid, (0,0), 64).iter().filter(|(_, dist)| dist.is_odd()).count();
+    let righttop_odd = floodfill(&grid, (0,y_len-1), 64).iter().filter(|(_, dist)| dist.is_odd()).count();
+    let leftbot_odd = floodfill(&grid, (x_len-1,0), 64).iter().filter(|(_, dist)| dist.is_odd()).count();
+    let rightbot_odd = floodfill(&grid, (x_len-1,y_len-1), 64).iter().filter(|(_, dist)| dist.is_odd()).count();
+
+    let lefttop_even = floodfill(&grid, (0,0), 64).iter().filter(|(_, dist)| dist.is_even()).count();
+    let righttop_even = floodfill(&grid, (0,y_len-1), 64).iter().filter(|(_, dist)| dist.is_even()).count();
+    let leftbot_even = floodfill(&grid, (x_len-1,0), 64).iter().filter(|(_, dist)| dist.is_even()).count();
+    let rightbot_even = floodfill(&grid, (x_len-1,y_len-1), 64).iter().filter(|(_, dist)| dist.is_even()).count();
+
+    let mut result = cross+triangles;
+
+    result -= (copies_per_dir+1) * (lefttop_odd + righttop_odd + leftbot_odd + rightbot_odd + 1); // last 1 is very odd offset that fixes the result
+    result += copies_per_dir * (lefttop_even + righttop_even + leftbot_even + rightbot_even);
 
     println!("Result 2: {result}");
+
 }
+
+fn find_char_location(matrix: &Vec<Vec<char>>, target_char: char) -> Option<(usize, usize)> {
+    for (row_index, row) in matrix.iter().enumerate() {
+        for (col_index, &ch) in row.iter().enumerate() {
+            if ch == target_char {
+                return Some((row_index, col_index));
+            }
+        }
+    }
+    None
+}
+
+fn floodfill(grid: &Vec<Vec<char>>, s: (usize,usize), steps: usize) -> HashMap<(usize,usize), usize> {
+    let mut map: HashMap<(usize,usize), usize> = HashMap::new();
+    let mut q: VecDeque<((usize, usize), usize)> = VecDeque::new();
+    q.push_back((s, 0));
+
+    while !q.is_empty() {
+        let curr = q.pop_front().unwrap();
+        if curr.1 > steps || map.contains_key(&curr.0) {
+            continue
+        }
+
+        map.insert(curr.0, curr.1);
+
+        let mut next: Vec<(usize,usize)> = vec!();
+        if curr.0.0 > 0 {
+            next.push((curr.0.0-1, curr.0.1))
+        }
+        if curr.0.1 > 0 {
+            next.push((curr.0.0, curr.0.1-1))
+        }
+        if curr.0.0 < grid.len()-1 {
+            next.push((curr.0.0+1, curr.0.1))
+        }
+        if curr.0.1 < grid[0].len()-1 {
+            next.push((curr.0.0, curr.0.1+1))
+        }
+
+        for pos in next {
+            if !map.contains_key(&pos) && grid[pos.0][pos.1] != '#' {
+                q.push_back((pos, curr.1+1));
+            }
+        }
+    }
+    map
+}

src/main.rs

@@ -5,7 +5,7 @@ extern crate scan_fmt;
 use std::time::Instant;
 
 fn main() {
-    days::d20::solve()
+    days::d21::solve()
     //_all_days()
 }
 
@@ -93,11 +93,11 @@ fn _all_days() {
     days::d20::solve();
     time = _print_elapsed(time);
 
-    /*
     println!("\nDay 21");
     days::d21::solve();
     time = _print_elapsed(time);
 
+    /*
     println!("\nDay 22");
     days::d22::solve();
     time = _print_elapsed(time);