feat(20/2024): solve second part

Author: manhunto

readme.md

@@ -30,7 +30,7 @@
 | [Day 17: Chronospatial Computer](src/solutions/year2024/day17.rs) |   -    |                - |                - |
 | [Day 18: RAM Run](src/solutions/year2024/day18.rs)                |   ⭐⭐   |            2.487 |          204.885 |
 | [Day 19: Linen Layout](src/solutions/year2024/day19.rs)           |   ⭐⭐   |            2.923 |           22.751 |
-| [Day 20: Race Condition](src/solutions/year2024/day20.rs)         |   ⭐    |            7.355 |                - |
+| [Day 20: Race Condition](src/solutions/year2024/day20.rs)         |   ⭐⭐   |            7.355 |          346.481 |
 
 # 2023
 

src/solutions/year2024/day18.rs

@@ -80,7 +80,7 @@ impl Default for Day18 {
 impl Day18 {
     fn new(grid_size: usize, memory_size: usize) -> Self {
         Self {
-            surface: SurfaceRange::from_points(0, grid_size as isize, 0, grid_size as isize),
+            surface: SurfaceRange::square(grid_size as isize),
             memory_size,
         }
     }

src/solutions/year2024/day20.rs

@@ -1,4 +1,5 @@
 use crate::solutions::Solution;
+use crate::utils::deltoid_surface::DeltoidSurface;
 use crate::utils::grid::Grid;
 use crate::utils::point::Point;
 use itertools::Itertools;
@@ -9,18 +10,46 @@ pub struct Day20;
 
 impl Solution for Day20 {
     fn part_one(&self, input: &str) -> String {
-        self.cheats_in_range(input, 100..).to_string()
+        self.part_one_cheats_in_range(input, 100..).to_string()
     }
 
-    fn part_two(&self, _input: &str) -> String {
-        String::from('0')
+    fn part_two(&self, input: &str) -> String {
+        // extract surface trait and contains method
+        // grid has function get every position in area
+        // rename surface range as rectangular area
+        //
+        self.part_two_cheats_in_range(input, 100..).to_string()
     }
 }
 
 impl Day20 {
-    fn cheats_in_range<R>(&self, input: &str, range: R) -> usize
+    fn part_one_cheats_in_range(&self, input: &str, range: impl RangeBounds<usize>) -> usize {
+        let cheat_range_from_current = |current: Point| {
+            current
+                .adjacent_vectors()
+                .map(|v| v.forward().position())
+                .into_iter()
+        };
+
+        self.cheats_in_range(input, range, &cheat_range_from_current)
+    }
+
+    fn part_two_cheats_in_range(&self, input: &str, range: impl RangeBounds<usize>) -> usize {
+        let cheat_range_from_current =
+            |current: Point| DeltoidSurface::new(current, 20).points().into_iter();
+
+        self.cheats_in_range(input, range, &cheat_range_from_current)
+    }
+
+    fn cheats_in_range<R, I>(
+        &self,
+        input: &str,
+        range: R,
+        cheat_positions: &dyn Fn(Point) -> I,
+    ) -> usize
     where
         R: RangeBounds<usize>,
+        I: Iterator<Item = Point>,
     {
         let grid: Grid<char> = Grid::from(input);
         let start = grid.get_first_position(&'S').unwrap();
@@ -32,30 +61,30 @@ impl Day20 {
             .path()
             .iter()
             .flat_map(|(current_time, current)| {
-                current
-                    .adjacent_vectors()
-                    .iter()
-                    .filter(|v| grid.is_for_point(&v.position(), '#'))
-                    .map(|p| p.forward())
+                cheat_positions(*current)
                     .filter(|v| {
-                        grid.get_for_point(&v.position())
+                        grid.get_for_point(v)
                             .is_some_and(|element| ['.', 'E'].contains(element))
                     })
-                    .filter_map(|v| {
-                        if let Some(time_after_cheat) =
-                            path_without_cheats.picoseconds_from(v.position())
-                        {
-                            if time_after_cheat > *current_time {
-                                return Some(time_after_cheat - current_time - 2);
-                                // why -2
+                    .filter_map(|cheat_position| {
+                        let time_after_cheat = path_without_cheats
+                            .picoseconds_from(cheat_position)
+                            .unwrap();
+                        let cheat_cost = current.manhattan_distance(&cheat_position) as usize;
+
+                        if time_after_cheat > *current_time + cheat_cost {
+                            let time = time_after_cheat - current_time - cheat_cost;
+                            if range.contains(&time) {
+                                return Some(time);
                             }
-                        }
 
-                        None
+                            None
+                        } else {
+                            None
+                        }
                     })
                     .collect_vec()
             })
-            .filter(|time| range.contains(time))
             .count()
     }
 
@@ -126,17 +155,28 @@ mod tests {
 ###############"#;
 
     #[test]
-    fn test_solve() {
-        assert_eq!(14, Day20.cheats_in_range(EXAMPLE, 2..=2));
-        assert_eq!(14, Day20.cheats_in_range(EXAMPLE, 4..=4));
-        assert_eq!(2, Day20.cheats_in_range(EXAMPLE, 6..=6));
-        assert_eq!(4, Day20.cheats_in_range(EXAMPLE, 8..=8));
-        assert_eq!(2, Day20.cheats_in_range(EXAMPLE, 10..=10));
-        assert_eq!(3, Day20.cheats_in_range(EXAMPLE, 12..=12));
-        assert_eq!(1, Day20.cheats_in_range(EXAMPLE, 20..=20));
-        assert_eq!(1, Day20.cheats_in_range(EXAMPLE, 36..=36));
-        assert_eq!(1, Day20.cheats_in_range(EXAMPLE, 38..=38));
-        assert_eq!(1, Day20.cheats_in_range(EXAMPLE, 40..=40));
-        assert_eq!(1, Day20.cheats_in_range(EXAMPLE, 64..=64));
+    fn part_one_cheats_in_range() {
+        assert_eq!(14, Day20.part_one_cheats_in_range(EXAMPLE, 2..=2));
+        assert_eq!(14, Day20.part_one_cheats_in_range(EXAMPLE, 4..=4));
+        assert_eq!(2, Day20.part_one_cheats_in_range(EXAMPLE, 6..=6));
+        assert_eq!(4, Day20.part_one_cheats_in_range(EXAMPLE, 8..=8));
+        assert_eq!(2, Day20.part_one_cheats_in_range(EXAMPLE, 10..=10));
+        assert_eq!(3, Day20.part_one_cheats_in_range(EXAMPLE, 12..=12));
+        assert_eq!(1, Day20.part_one_cheats_in_range(EXAMPLE, 20..=20));
+        assert_eq!(1, Day20.part_one_cheats_in_range(EXAMPLE, 36..=36));
+        assert_eq!(1, Day20.part_one_cheats_in_range(EXAMPLE, 38..=38));
+        assert_eq!(1, Day20.part_one_cheats_in_range(EXAMPLE, 40..=40));
+        assert_eq!(1, Day20.part_one_cheats_in_range(EXAMPLE, 64..=64));
+    }
+
+    #[test]
+    fn part_two_cheats_in_range() {
+        assert_eq!(32, Day20.part_two_cheats_in_range(EXAMPLE, 50..=50));
+        assert_eq!(31, Day20.part_two_cheats_in_range(EXAMPLE, 52..=52));
+        assert_eq!(29, Day20.part_two_cheats_in_range(EXAMPLE, 54..=54));
+        assert_eq!(39, Day20.part_two_cheats_in_range(EXAMPLE, 56..=56));
+        assert_eq!(25, Day20.part_two_cheats_in_range(EXAMPLE, 58..=58));
+        assert_eq!(23, Day20.part_two_cheats_in_range(EXAMPLE, 60..=60));
+        assert_eq!(20, Day20.part_two_cheats_in_range(EXAMPLE, 62..=62));
     }
 }

src/utils/deltoid_surface.rs

@@ -0,0 +1,102 @@
+use crate::utils::point::Point;
+use crate::utils::range::Range;
+use std::collections::HashMap;
+
+type Ranges = HashMap<isize, Range>;
+
+pub struct DeltoidSurface {
+    #[allow(dead_code)]
+    point: Point,
+    #[allow(dead_code)]
+    distance: usize,
+    #[allow(dead_code)]
+    ranges: Ranges,
+    points: Vec<Point>,
+}
+
+impl DeltoidSurface {
+    pub fn new(point: Point, distance: usize) -> Self {
+        let ranges = Self::build_ranges(point, distance);
+        let points = Self::build_points(&ranges);
+
+        Self {
+            point,
+            distance,
+            ranges,
+            points,
+        }
+    }
+
+    pub fn points(&self) -> Vec<Point> {
+        self.points.clone()
+    }
+
+    fn build_ranges(point: Point, distance: usize) -> Ranges {
+        let isize_distance = distance as isize;
+
+        let mut ranges: Ranges = Ranges::with_capacity(distance * 2 + 1);
+
+        for x in -isize_distance..=isize_distance {
+            let height_diff = isize_distance - x.abs();
+            let x = point.x + x;
+            let y_range = Range::new(point.y - height_diff, point.y + height_diff).unwrap();
+
+            ranges.insert(x, y_range);
+        }
+
+        ranges
+    }
+
+    fn build_points(ranges: &Ranges) -> Vec<Point> {
+        ranges
+            .iter()
+            .flat_map(|(x, y_range)| {
+                y_range
+                    .iter()
+                    .map(|y| Point::new(*x, y))
+                    .collect::<Vec<Point>>()
+            })
+            .collect()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::utils::deltoid_surface::DeltoidSurface;
+    use crate::utils::grid::Grid;
+    use crate::utils::point::Point;
+    use crate::utils::surface_range::SurfaceRange;
+
+    #[test]
+    fn deltoid_surface_visual_test() {
+        const EXPECTED: &str = r#"........
+....#...
+...###..
+..#####.
+...###..
+....#...
+........
+........"#;
+
+        let expected_grid: Grid<char> = Grid::from(EXPECTED);
+        let surface = DeltoidSurface::new(Point::new(4, 3), 2);
+
+        let mut current_grid: Grid<char> = Grid::filled(SurfaceRange::square(7), '.');
+        current_grid.modify_many(surface.points(), '#');
+
+        assert_eq!(expected_grid.to_string(), current_grid.to_string());
+    }
+
+    #[test]
+    fn manhattan_distance_is_at_most_distance() {
+        let middle = Point::new(4, 3);
+        let distance = 3;
+
+        let surface = DeltoidSurface::new(middle, distance);
+
+        assert!(surface
+            .points
+            .iter()
+            .all(|p| p.manhattan_distance(&middle) <= distance as isize));
+    }
+}

src/utils/mod.rs

@@ -1,4 +1,5 @@
 pub mod chain_pattern_finder;
+pub mod deltoid_surface;
 pub mod direction;
 pub mod graphs;
 pub mod grid;

src/utils/surface_range.rs

@@ -21,6 +21,10 @@ impl SurfaceRange {
         )
     }
 
+    pub fn square(size: isize) -> Self {
+        Self::from_points(0, size, 0, size)
+    }
+
     pub fn x(&self) -> Range {
         self.x_range
     }
@@ -89,7 +93,7 @@ mod tests {
 
     #[test]
     fn shrink() {
-        let surface_range = SurfaceRange::from_points(0, 10, 0, 10);
+        let surface_range = SurfaceRange::square(10);
         let shrunk = surface_range._shrink(1);
 
         let expected = SurfaceRange::from_points(1, 9, 1, 9);