ditched the multiple threads, because that wasn't valid

README.md

@@ -21,4 +21,5 @@ running:
 *solution2*
 * written in rust
 * single and multiple drones
+* uses basically the same method, but after a definitive flight path is calculated, the grid is updated for the next drone
 * see tests and main for validity of the algorithm

solution2/src/algorithm.rs

@@ -3,10 +3,6 @@ use rand::Rng;
 use std::collections::HashSet;
 use std::hash::{DefaultHasher, Hash, Hasher};
 use std::time::SystemTime;
-use std::{
-    sync::{Arc, Mutex},
-    thread,
-};
 
 #[allow(non_snake_case)]
 pub fn find_optimal_path_for_n_drones(
@@ -16,25 +12,26 @@ pub fn find_optimal_path_for_n_drones(
     t: usize,
     T: u128,
 ) -> PathsResult {
-    let arc = Arc::new(Mutex::new(grid));
+    // multiple drones are calculated one after another
-
+    // grid hits must be updated for the next drone after the optimal for the previous has been calculated
-    let mut handles = vec![];
 
+    let mut paths = vec![];
+    let mut grid = grid.clone();
     for _ in 0..ndrones {
-        let gridref = Arc::clone(&arc);
+        let mut current_grid = grid.clone();
-
         let mut rng = rand::thread_rng();
         // start at random position
         let x: u16 = rng.gen_range(0..N);
         let y: u16 = rng.gen_range(0..N);
-        // start new thread for a single drone
+        // divide max algorithm time by number of drones
-        let handle = thread::spawn(move || find_optimal_path(gridref, N, t, T, x, y));
+        let time_per_drone = T / ndrones as u128;
-        handles.push(handle);
+        let optimal = find_optimal_path(&mut current_grid, N, t, time_per_drone, x, y);
-    }
 
-    let mut paths = vec![];
+        // update the grid to the lastes state
-    for handle in handles {
+        for (index, p) in optimal.points.iter().enumerate() {
-        paths.push(handle.join().unwrap());
+            grid.hit(p.x, p.y, index);
+        }
+        paths.push(optimal);
     }
 
     let overall_score = paths.iter().map(|p| p.value).sum();
@@ -52,19 +49,12 @@ pub fn find_optimal_path_for_n_drones(
 /// T max duration of the algorithm
 /// x,y drone start position in the grid
 #[allow(non_snake_case)]
-pub fn find_optimal_path(
+pub fn find_optimal_path(grid: &mut Grid, N: u16, t: usize, T: u128, x: u16, y: u16) -> Path {
-    grid: Arc<Mutex<Grid>>,
-    N: u16,
-    t: usize,
-    T: u128,
-    x: u16,
-    y: u16,
-) -> Path {
     let mut paths_to_consider: Vec<Path> = Vec::new();
     let mut taken_paths: HashSet<u64> = HashSet::new();
 
     // starting point
-    let path = Path::new(Arc::clone(&grid), x, y);
+    let path = Path::new(grid, x, y);
 
     // always current max
     let mut max: Path = path.clone(); // sorry
@@ -101,97 +91,90 @@ pub fn find_optimal_path(
 
         // create a list of directions to take
         new_directions.clear();
-        {
+        if y > 0 {
-            let arc = Arc::clone(&grid);
+            new_directions.push(Point::new(
-            let mut lock = arc.lock();
+                x,
-            let grid = lock.as_mut().unwrap();
+                y - 1,
-            if y > 0 {
+                grid.get_value(x, y - 1, Some(&current_path)),
-                new_directions.push(Point::new(
+            ));
-                    x,
-                    y - 1,
-                    grid.get_value(x, y - 1, current_path.length() + 1),
-                ));
-                if x < N - 1 {
-                    new_directions.push(Point::new(
-                        x + 1,
-                        y - 1,
-                        grid.get_value(x + 1, y - 1, current_path.length() + 1),
-                    ));
-                }
-            }
-
-            if x > 0 {
-                new_directions.push(Point::new(
-                    x - 1,
-                    y,
-                    grid.get_value(x - 1, y, current_path.length() + 1),
-                ));
-                if y > 0 {
-                    new_directions.push(Point::new(
-                        x - 1,
-                        y - 1,
-                        grid.get_value(x - 1, y - 1, current_path.length() + 1),
-                    ));
-                }
-            }
-
             if x < N - 1 {
                 new_directions.push(Point::new(
                     x + 1,
-                    y,
+                    y - 1,
-                    grid.get_value(x + 1, y, current_path.length() + 1),
+                    grid.get_value(x + 1, y - 1, Some(&current_path)),
                 ));
-                if y < N - 1 {
-                    new_directions.push(Point::new(
-                        x + 1,
-                        y + 1,
-                        grid.get_value(x + 1, y + 1, current_path.length() + 1),
-                    ));
-                }
             }
+        }
 
+        if x > 0 {
+            new_directions.push(Point::new(
+                x - 1,
+                y,
+                grid.get_value(x - 1, y, Some(&current_path)),
+            ));
+            if y > 0 {
+                new_directions.push(Point::new(
+                    x - 1,
+                    y - 1,
+                    grid.get_value(x - 1, y - 1, Some(&current_path)),
+                ));
+            }
+        }
+
+        if x < N - 1 {
+            new_directions.push(Point::new(
+                x + 1,
+                y,
+                grid.get_value(x + 1, y, Some(&current_path)),
+            ));
             if y < N - 1 {
                 new_directions.push(Point::new(
-                    x,
+                    x + 1,
                     y + 1,
-                    grid.get_value(x, y + 1, current_path.length() + 1),
+                    grid.get_value(x + 1, y + 1, Some(&current_path)),
                 ));
-                if x > 0 {
+            }
-                    new_directions.push(Point::new(
+        }
-                        x - 1,
+
-                        y + 1,
+        if y < N - 1 {
-                        grid.get_value(x - 1, y + 1, current_path.length() + 1),
+            new_directions.push(Point::new(
-                    ));
+                x,
+                y + 1,
+                grid.get_value(x, y + 1, Some(&current_path)),
+            ));
+            if x > 0 {
+                new_directions.push(Point::new(
+                    x - 1,
+                    y + 1,
+                    grid.get_value(x - 1, y + 1, Some(&current_path)),
+                ));
+            }
+        }
+
+        let mut points_added = false;
+        for point in new_directions.iter() {
+            if point.value > 0.0 {
+                let mut new_path = current_path.clone();
+                new_path.add(point.clone());
+
+                let mut s = DefaultHasher::new();
+                new_path.hash(&mut s);
+                let hash = s.finish();
+
+                if !taken_paths.contains(&hash) {
+                    points_added = true;
+                    grid.hit(point.x, point.y, new_path.length());
+                    paths_to_consider.push(new_path);
+                    taken_paths.insert(hash);
                 }
             }
-
+        }
-            let mut points_added = false;
+        if !points_added {
-            for point in new_directions.iter() {
+            // dead end, evict
-                if point.value > 0.0 {
+            let ended = paths_to_consider.pop().unwrap();
-                    let mut new_path = current_path.clone();
+            if ended.value > max.value {
-                    new_path.add(point.clone());
+                max = ended;
-
-                    let mut s = DefaultHasher::new();
-                    new_path.hash(&mut s);
-                    let hash = s.finish();
-
-                    if !taken_paths.contains(&hash) {
-                        points_added = true;
-                        grid.hit(point.x, point.y, new_path.length());
-                        paths_to_consider.push(new_path);
-                        taken_paths.insert(hash);
-                    }
-                }
             }
-            if !points_added {
-                // dead end, evict
-                let ended = paths_to_consider.pop().unwrap();
-                if ended.value > max.value {
-                    max = ended;
-                }
-            }
-
-            //drop lock
         }
 
         // continue?
@@ -211,8 +194,9 @@ mod tests {
 
     #[test]
     pub fn test_single_drone() {
-        let grid = Grid::new(20);
+        let mut grid = Grid::new(100);
-        let opt = find_optimal_path(Arc::new(Mutex::new(grid.clone())), 100, 10, 1000, 9, 9);
+        // values for x and y are chosen so that a loop must occur
+        let opt = find_optimal_path(&mut grid, 20, 20, 1000, 9, 9);
 
         let mut all_points: HashSet<Point> = HashSet::new();
         let mut loop_in_path = false;
@@ -225,12 +209,14 @@ mod tests {
             all_points.insert(point.clone());
         }
         if loop_in_path {
-            //println!("check"); //verify that this occurs
+            println!("check"); //verify that this occurs
             let max_sum: f32 = opt
                 .points
                 .iter()
                 .map(|p| grid.get_initial_value(p.x, p.y))
                 .sum();
+            println!("max sum {:?}, opt path {:?}", max_sum, opt);
+            // verify that the grid value was updated because of the hit
             assert!(max_sum > opt.value());
         }
     }

solution2/src/grid.rs

@@ -1,8 +1,7 @@
 use std::{
     cmp::Ordering,
-    collections::{BTreeSet, HashMap, LinkedList},
+    collections::{HashMap, HashSet, LinkedList},
     hash::{Hash, Hasher},
-    sync::{Arc, Mutex},
 };
 
 const RECOVERY_FACTOR: f32 = 0.1;
@@ -12,9 +11,9 @@ const RECOVERY_FACTOR: f32 = 0.1;
 pub struct Grid {
     data: Vec<Vec<u16>>,
     // keep track of every point that has been hit at some time
-    hits: HashMap<(u16, u16), BTreeSet<usize>>, // TreeSet<usize> is integer times that point has been visited.
+    hits: HashMap<(u16, u16), usize>, // TreeSet<usize> is integer times that point has been visited.
-                                                // Must always be sorted and could probably be a single int
+                                      // Must always be sorted and could probably be a single int
-                                                // (keep track of last time hit)
+                                      // (keep track of last time hit)
 }
 
 impl Grid {
@@ -51,30 +50,47 @@ impl Grid {
         *(self.data.get(y as usize).unwrap().get(x as usize).unwrap()) as f32
     }
 
-    pub fn get_value(&self, x: u16, y: u16, time: usize) -> f32 {
+    /// get the value of a point on the grid
-        let hit = self.hits.get(&(x, y));
+    /// 1. initial value, given by the datafile
-
+    /// 2. value possibly updated by a previous drone in the multiple drone scenario
+    /// 3. value possibly updated by the drone itself, when it gets to a point that it already occupied
+    pub fn get_value(&self, x: u16, y: u16, path: Option<&Path>) -> f32 {
+        let pathlen = path.map_or(0, |p| p.length());
         let initial_value = self.get_initial_value(x, y);
 
-        if let Some(hit_times) = hit {
+        // 1.
-            for t in hit_times.iter().rev() {
+        let mut value = initial_value;
-                if time > *t {
+
-                    let elapsed_since_hit = (time - *t) as f32;
+        // 2.
-                    let value = f32::min(
+        let hit_time = self.hits.get(&(x, y));
-                        elapsed_since_hit * initial_value * RECOVERY_FACTOR,
+        if let Some(hit_time) = hit_time {
-                        initial_value,
+            if pathlen > *hit_time {
-                    );
+                // +1 because we are in the process of adding a new point to the path
-                    return value;
+                let elapsed_since_hit = (pathlen + 1 - hit_time) as f32;
-                }
+                value = f32::min(
+                    elapsed_since_hit * initial_value * RECOVERY_FACTOR,
+                    initial_value,
+                );
             }
-            0.0
-        } else {
-            initial_value
         }
+
+        // 3.
+        if let Some(path) = path {
+            let maybe_hit = path.points_lookup.get(&(x, y));
+            if let Some(hit_time) = maybe_hit {
+                let elapsed_since_hit = (path.points.len() - hit_time) as f32;
+                value = f32::min(
+                    elapsed_since_hit * initial_value * RECOVERY_FACTOR,
+                    initial_value,
+                );
+            }
+        }
+
+        value
     }
 
     pub fn hit(&mut self, x: u16, y: u16, time: usize) {
-        self.hits.entry((x, y)).or_default().insert(time);
+        self.hits.insert((x, y), time);
     }
 
     pub fn size(&self) -> u16 {
@@ -85,15 +101,13 @@ impl Grid {
 #[derive(Debug, Clone)]
 pub struct Path {
     pub points: LinkedList<Point>,
+    pub points_lookup: HashMap<(u16, u16), usize>,
     pub value: f32,
 }
 
 impl Path {
-    pub fn new(grid: Arc<Mutex<Grid>>, initial_x: u16, initial_y: u16) -> Self {
+    pub fn new(grid: &Grid, initial_x: u16, initial_y: u16) -> Self {
-        let mut points = LinkedList::new();
+        let value = grid.get_value(initial_x, initial_y, None);
-        let mut lock = grid.lock();
-        let grid = lock.as_mut().unwrap();
-        let value = grid.get_value(initial_x, initial_y, 0);
 
         let p = Point {
             x: initial_x,
@@ -101,8 +115,16 @@ impl Path {
             value,
         };
 
+        let mut points = LinkedList::new();
         points.push_front(p);
-        Self { points, value }
+        let mut points_lookup = HashMap::new();
+        points_lookup.insert((initial_x, initial_y), 0);
+
+        Self {
+            points,
+            value,
+            points_lookup,
+        }
     }
 
     // length = age of the path
@@ -204,8 +226,8 @@ mod test {
     #[test]
     pub fn test() {
         let grid = Grid::new(20);
-        assert_eq!(grid.get_value(0, 0, 0), 0.0);
+        assert_eq!(grid.get_value(0, 0, None), 0.0);
-        assert_eq!(grid.get_value(0, 1, 0), 1.0);
+        assert_eq!(grid.get_value(0, 1, None), 1.0);
     }
 }
 

solution2/src/main.rs

@@ -1,8 +1,9 @@
 use solution2::{algorithm::find_optimal_path_for_n_drones, grid::Grid};
 
-/// this app calculates paths for 4 drones, concurrently, with a shared grid
+/// this app calculates paths for 4 drones
 fn main() {
-    let result = find_optimal_path_for_n_drones(Grid::new(100), 4, 100, 15, 2000);
+    let grid = Grid::new(100);
+    let result = find_optimal_path_for_n_drones(grid, 4, 100, 15, 2000);
     for (i, path) in result.paths.iter().enumerate() {
         println!("path {}: score {}", i, path.value())
     }