Solve day 20

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+#.###.#.###.#.###.#.###.#.#.###.#.###.#.###.#.###.###.###.#.#.#.#.###.#.#####.#.#.#.###.#.#.#.#.#.#.###.#####.#.#.#.#######.#.###.#.#.###.#.#
+#.....#.....#.....#.....#...###...###...###...###.....###...#...#.....#.......#...#.....#...#...#...###.......#...#.........#.....#...###...#
+#############################################################################################################################################

src/bin/20.rs

@@ -0,0 +1,149 @@
+use std::collections::HashMap;
+
+use itertools::Itertools;
+
+static DIRECTIONS: [(isize, isize); 4] = [(0, -1), (1, 0), (0, 1), (-1, 0)];
+
+static CHEATPOS1: [(isize, isize); 8] = [
+    (0, 2),
+    (1, 1),
+    (2, 0),
+    (1, -1),
+    (0, -2),
+    (-1, -1),
+    (-2, 0),
+    (-1, 1),
+];
+
+fn main() {
+    let text = std::fs::read_to_string("input/20-1.in").unwrap();
+
+    let mut startx = 0;
+    let mut starty = 0;
+
+    let map = text
+        .lines()
+        .enumerate()
+        .map(|(y, l)| {
+            l.chars()
+                .enumerate()
+                .map(|(x, c)| match c {
+                    '#' => false,
+                    '.' => true,
+                    'S' => {
+                        startx = x;
+                        starty = y;
+                        true
+                    }
+                    'E' => true,
+                    _ => unreachable!(),
+                })
+                .collect::<Vec<_>>()
+        })
+        .collect::<Vec<_>>();
+
+    let mut path = vec![(startx, starty)];
+
+    while let Some((x, y)) = DIRECTIONS
+        .iter()
+        .filter_map(|&(dx, dy)| {
+            let &(lastx, lasty) = path.last()?;
+            let nx = lastx.checked_add_signed(dx)?;
+            let ny = lasty.checked_add_signed(dy)?;
+
+            if path
+                .last_chunk::<2>()
+                .is_some_and(|&[(px, py), _]| px == nx && py == ny)
+            {
+                return None;
+            }
+
+            if map[ny][nx] {
+                Some((nx, ny))
+            } else {
+                None
+            }
+        })
+        .next()
+    {
+        path.push((x, y));
+    }
+
+    let path_map = path
+        .iter()
+        .enumerate()
+        .map(|(i, &d)| (d, i))
+        .collect::<HashMap<_, _>>();
+
+    let t = path
+        .iter()
+        .cartesian_product(CHEATPOS1)
+        .filter_map(|(&(sx, sy), (dx, dy))| {
+            let endx = sx.checked_add_signed(dx)?;
+            let endy = sy.checked_add_signed(dy)?;
+
+            if endx < map[0].len() && endy < map.len() && map[endy][endx] {
+                if path_map[&(endx, endy)] > 2 + path_map[&(sx, sy)] {
+                    Some((
+                        (sx, sy),
+                        (endx, endy),
+                        path_map[&(endx, endy)] - 2 - path_map[&(sx, sy)],
+                    ))
+                } else {
+                    None
+                }
+            } else {
+                None
+            }
+        })
+        .map(|(_, _, c)| c)
+        .filter(|&c| c >= 100)
+        .count();
+
+    println!("{t}");
+
+    let duration = 20isize;
+    let cheatpos2 = (-duration..=duration)
+        .cartesian_product(-duration..=duration)
+        .filter(|&(dx, dy)| dx.abs() + dy.abs() <= duration)
+        .collect::<Vec<_>>();
+
+    let t = path
+        .iter()
+        .cartesian_product(cheatpos2)
+        .filter_map(|(&(sx, sy), (dx, dy))| {
+            let endx = sx.checked_add_signed(dx)?;
+            let endy = sy.checked_add_signed(dy)?;
+
+            let len = (dx.abs() + dy.abs()) as usize;
+
+            if endx < map[0].len() && endy < map.len() && map[endy][endx] {
+                if path_map[&(endx, endy)] > len + path_map[&(sx, sy)] {
+                    Some((
+                        (sx, sy),
+                        (endx, endy),
+                        path_map[&(endx, endy)] - len - path_map[&(sx, sy)],
+                    ))
+                } else {
+                    None
+                }
+            } else {
+                None
+            }
+        })
+        // .inspect(|d| {
+        //     if d.0 .0 == 1 && d.0 .1 == 3 {
+        //         dbg!(d);
+        //     }
+        // })
+        .map(|(_, _, c)| c)
+        // .filter(|&c| c >= 50)
+        // .counts();
+        .filter(|&c| c >= 100)
+        .count();
+
+    // let mut t = t.iter().collect::<Vec<_>>();
+    // t.sort();
+    // dbg!(t);
+    println!("{t}");
+}