ditched the multiple threads, because that wasn't valid

README.md

@@ -0,0 +1,25 @@
+**find optimal optimal path for drones in a grid of assigned values**
+
+*solution1*
+* written in java
+* single drone solution
+* employs a floodfill algorithm
+* where possible paths are always sorted in descending order of value (so far) of the points in the path
+* and which uses backtracking to find alternative paths that may be of higher value
+* non-recursivity ensures no issues for large grids
+* the algorithm is embedded in a rest api
+* it also has a html canvas frontend that draws the path on the grid
+
+running:
+* install jdk22, and apache maven
+* run `mvn spring-boot:run`
+* go to http://localhost:8080
+* in the console in the ui type `fly` [enter]
+* input values for the algorithm can be updated, eg `T=2000` or `x=10` etc.
+* use `clear` to refresh
+
+*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

@@ -0,0 +1,223 @@
+use crate::grid::{Grid, Path, PathsResult, Point};
+use rand::Rng;
+use std::collections::HashSet;
+use std::hash::{DefaultHasher, Hash, Hasher};
+use std::time::SystemTime;
+
+#[allow(non_snake_case)]
+pub fn find_optimal_path_for_n_drones(
+    grid: Grid,
+    ndrones: usize,
+    N: u16,
+    t: usize,
+    T: u128,
+) -> PathsResult {
+    // 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 paths = vec![];
+    let mut grid = grid.clone();
+    for _ in 0..ndrones {
+        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);
+        // divide max algorithm time by number of drones
+        let time_per_drone = T / ndrones as u128;
+        let optimal = find_optimal_path(&mut current_grid, N, t, time_per_drone, x, y);
+
+        // update the grid to the lastes state
+        for (index, p) in optimal.points.iter().enumerate() {
+            grid.hit(p.x, p.y, index);
+        }
+        paths.push(optimal);
+    }
+
+    let overall_score = paths.iter().map(|p| p.value).sum();
+
+    PathsResult {
+        paths,
+        overall_score,
+    }
+}
+
+/// finds the optimal path for a drone in a grid of points(x,y) that each has a fixed initial value
+/// observing a point (hit) resets the value to 0, after wich it gradually increases with time in a fixed rate
+/// N size of square grid (rows and cols)
+/// t max length of a flight path
+/// T max duration of the algorithm
+/// x,y drone start position in the grid
+#[allow(non_snake_case)]
+pub fn find_optimal_path(grid: &mut 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(grid, x, y);
+
+    // always current max
+    let mut max: Path = path.clone(); // sorry
+
+    // add the first path
+    paths_to_consider.push(path);
+
+    // keep track of time
+    let t0 = SystemTime::now();
+    let mut running = true;
+
+    // will keep at most 8 new directions from current location
+    let mut new_directions = vec![];
+
+    let mut current_path;
+    while running && !paths_to_consider.is_empty() {
+        // would have liked a list like datastructure that is guaranteed to be sorted
+        // BTreeSet would be nice, but equals/hash/cmp calls would be unneeded overhead
+        paths_to_consider.sort(); // but this is also overhead compared to BTreeSet
+        current_path = paths_to_consider.last().unwrap().clone(); // assert = Some
+
+        // evict paths that are of max len
+        while current_path.length() >= t {
+            _ = paths_to_consider.pop(); // discards element that = current_path
+            if current_path.value() > max.value() {
+                max = current_path.clone(); // sorry
+            }
+            current_path = paths_to_consider.last().unwrap().clone();
+        }
+
+        let head = current_path.last();
+        let x = head.x;
+        let y = head.y;
+
+        // create a list of directions to take
+        new_directions.clear();
+        if y > 0 {
+            new_directions.push(Point::new(
+                x,
+                y - 1,
+                grid.get_value(x, y - 1, Some(&current_path)),
+            ));
+            if x < N - 1 {
+                new_directions.push(Point::new(
+                    x + 1,
+                    y - 1,
+                    grid.get_value(x + 1, y - 1, Some(&current_path)),
+                ));
+            }
+        }
+
+        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 + 1,
+                    y + 1,
+                    grid.get_value(x + 1, y + 1, Some(&current_path)),
+                ));
+            }
+        }
+
+        if y < N - 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);
+                }
+            }
+        }
+        if !points_added {
+            // dead end, evict
+            let ended = paths_to_consider.pop().unwrap();
+            if ended.value > max.value {
+                max = ended;
+            }
+        }
+
+        // continue?
+        let t1 = SystemTime::now();
+        if let Ok(elapsed) = t1.duration_since(t0) {
+            if elapsed.as_millis() > T {
+                running = false;
+            }
+        }
+    }
+    max
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    pub fn test_single_drone() {
+        let mut grid = Grid::new(100);
+        // 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;
+        for point in opt.points.iter() {
+            if all_points.contains(point) {
+                // we have a path that crosses itself
+                // path value should be less than sum of individual initial values of point
+                loop_in_path = true
+            }
+            all_points.insert(point.clone());
+        }
+        if loop_in_path {
+            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

@@ -1,18 +1,19 @@
 use std::{
     cmp::Ordering,
-    collections::{BTreeSet, HashMap, LinkedList},
+    collections::{HashMap, HashSet, LinkedList},
     hash::{Hash, Hasher},
-    sync::{Arc, Mutex},
 };
 
+const RECOVERY_FACTOR: f32 = 0.1;
+
 #[allow(non_snake_case)]
-#[derive(Debug)]
+#[derive(Debug, Clone)]
 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.
-                                                // Must always be sorted and could probably be a single int
-                                                // (keep track of last time hit)
+    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
+                                      // (keep track of last time hit)
 }
 
 impl Grid {
@@ -45,27 +46,51 @@ impl Grid {
         }
     }
 
-    pub fn get_value(&self, x: u16, y: u16, time: usize) -> f32 {
-        let hit = self.hits.get(&(x, y));
+    pub fn get_initial_value(&self, x: u16, y: u16) -> f32 {
+        *(self.data.get(y as usize).unwrap().get(x as usize).unwrap()) as f32
+    }
 
-        let initial_value = *(self.data.get(y as usize).unwrap().get(x as usize).unwrap()) as f32;
+    /// get the value of a point on the grid
+    /// 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 {
-            for t in hit_times.iter().rev() {
-                if time > *t {
-                    let elapsed_since_hit = (time - *t) as f32;
+        // 1.
+        let mut value = initial_value;
 
-                    return f32::min(elapsed_since_hit * initial_value * 0.1, initial_value);
-                }
+        // 2.
+        let hit_time = self.hits.get(&(x, y));
+        if let Some(hit_time) = hit_time {
+            if pathlen > *hit_time {
+                // +1 because we are in the process of adding a new point to the path
+                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 {
@@ -75,16 +100,14 @@ impl Grid {
 
 #[derive(Debug, Clone)]
 pub struct Path {
-    points: LinkedList<Point>,
+    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 {
-        let mut points = LinkedList::new();
-        let mut lock = grid.lock();
-        let grid = lock.as_mut().unwrap();
-        let value = grid.get_value(initial_x, initial_y, 0);
+    pub fn new(grid: &Grid, initial_x: u16, initial_y: u16) -> Self {
+        let value = grid.get_value(initial_x, initial_y, None);
 
         let p = Point {
             x: initial_x,
@@ -92,10 +115,19 @@ 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
     pub fn length(&self) -> usize {
         self.points.len()
     }
@@ -194,7 +226,13 @@ 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, 1, 0), 1.0);
+        assert_eq!(grid.get_value(0, 0, None), 0.0);
+        assert_eq!(grid.get_value(0, 1, None), 1.0);
     }
 }
+
+#[derive(Debug)]
+pub struct PathsResult {
+    pub paths: Vec<Path>,
+    pub overall_score: f32,
+}

solution2/src/lib.rs

@@ -1,180 +1,2 @@
-use grid::{Grid, Path, Point};
-use std::collections::HashSet;
-use std::hash::{DefaultHasher, Hash, Hasher};
-use std::sync::{Arc, Mutex};
-use std::time::SystemTime;
-
+pub mod algorithm;
 pub mod grid;
-
-/// finds the optimal path for a drone in a grid of points(x,y) that each has a fixed initial value
-/// observing a point (hit) resets the value to 0, after wich it gradually increases with time in a fixed rate
-/// N size of square grid (rows and cols)
-/// t max length of a flight path
-/// T max duration of the algorithm
-/// x,y drone start position in the grid
-#[allow(non_snake_case)]
-pub fn find_optimal_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);
-
-    // always current max
-    let mut max: Path = path.clone(); // sorry
-
-    // add the first path
-    paths_to_consider.push(path);
-
-    // keep track of time
-    let t0 = SystemTime::now();
-    let mut running = true;
-
-    // this is time spent for the path, grid keeps the global timeframe
-    // same as path length, so remove?
-    let mut discrete_elapsed = 0;
-
-    // will keep at most 8 new directions from current location
-    let mut new_directions = vec![];
-
-    let mut current_path;
-    while running && !paths_to_consider.is_empty() {
-        paths_to_consider.sort();
-        current_path = paths_to_consider.last().unwrap().clone(); // assert = Some
-
-        // evict paths that are of max len
-        while current_path.length() >= t {
-            _ = paths_to_consider.remove(paths_to_consider.len() - 1);
-            if current_path.value() > max.value() {
-                max = current_path.clone(); // sorry
-            }
-            current_path = paths_to_consider.last().unwrap().clone();
-        }
-
-        let head = current_path.last();
-        let x = head.x;
-        let y = head.y;
-
-        // create a list of directions to take
-        new_directions.clear();
-        {
-            let arc = Arc::clone(&grid);
-            let mut lock = arc.lock();
-            let grid = lock.as_mut().unwrap();
-            if y > 0 {
-                new_directions.push(Point::new(
-                    x,
-                    y - 1,
-                    grid.get_value(x, y - 1, discrete_elapsed),
-                ));
-                if x < N - 1 {
-                    new_directions.push(Point::new(
-                        x + 1,
-                        y - 1,
-                        grid.get_value(x + 1, y - 1, discrete_elapsed),
-                    ));
-                }
-            }
-
-            if x > 0 {
-                new_directions.push(Point::new(
-                    x - 1,
-                    y,
-                    grid.get_value(x - 1, y, discrete_elapsed),
-                ));
-                if y > 0 {
-                    new_directions.push(Point::new(
-                        x - 1,
-                        y - 1,
-                        grid.get_value(x - 1, y - 1, discrete_elapsed),
-                    ));
-                }
-            }
-
-            if x < N - 1 {
-                new_directions.push(Point::new(
-                    x + 1,
-                    y,
-                    grid.get_value(x + 1, y, discrete_elapsed),
-                ));
-                if y < N - 1 {
-                    new_directions.push(Point::new(
-                        x + 1,
-                        y + 1,
-                        grid.get_value(x + 1, y + 1, discrete_elapsed),
-                    ));
-                }
-            }
-
-            if y < N - 1 {
-                new_directions.push(Point::new(
-                    x,
-                    y + 1,
-                    grid.get_value(x, y + 1, discrete_elapsed),
-                ));
-                if x > 0 {
-                    new_directions.push(Point::new(
-                        x - 1,
-                        y + 1,
-                        grid.get_value(x - 1, y + 1, discrete_elapsed),
-                    ));
-                }
-            }
-
-            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, discrete_elapsed);
-                        paths_to_consider.push(new_path);
-                        taken_paths.insert(hash);
-                    }
-                }
-            }
-            if !points_added {
-                // dead end, evict
-                let ended = paths_to_consider.remove(paths_to_consider.len() - 1);
-                if ended.value > max.value {
-                    max = ended;
-                }
-            }
-        }
-
-        // continue?
-        let t1 = SystemTime::now();
-        if let Ok(elapsed) = t1.duration_since(t0) {
-            if elapsed.as_millis() > T {
-                running = false;
-            }
-        }
-        discrete_elapsed += 1;
-    }
-    max
-}
-
-#[cfg(test)]
-mod tests {
-    use super::*;
-
-    #[test]
-    pub fn test() {
-        let mut grid = Grid::new(20);
-        let opt = find_optimal_path(Arc::new(Mutex::new(grid)), 100, 10, 1000, 9, 9);
-        println!("value {:?}", opt);
-    }
-}

solution2/src/main.rs

@@ -1,36 +1,11 @@
-use rand::Rng;
-use solution2::{find_optimal_path, grid::Grid};
-use std::{
-    sync::{Arc, Mutex},
-    thread,
-};
+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() {
-    find_optimal_path_for_n_drones(4, 100, 10, 1000);
-}
-
-#[allow(non_snake_case)]
-pub fn find_optimal_path_for_n_drones(ndrones: usize, N: u16, t: usize, T: u128) {
     let grid = Grid::new(100);
-    let arc = Arc::new(Mutex::new(grid));
-
-    let mut handles = vec![];
-
-    for _ in 0..ndrones {
-        let gridref = Arc::clone(&arc);
-
-        let mut rng = rand::thread_rng();
-        // start at random position
-        let x: u16 = rng.gen_range(0..100);
-        let y: u16 = rng.gen_range(0..100);
-        // start new thread for a single drone
-        let handle = thread::spawn(move || find_optimal_path(gridref, N, t, T, x, y));
-        handles.push(handle);
-    }
-
-    for handle in handles {
-        let result = handle.join().unwrap();
-        println!("{result:?}");
+    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())
     }
+    println!("overall: {}", result.overall_score);
 }