Change A* heuristic to be a proper estimate

This makes it:
- Actually find the path with the fewest number of moves, and
- Not be so prone to getting stuck exploring space that seems "close to
  a solution" but is actually a dead end.

src/main.rs

@@ -78,12 +78,6 @@ impl<const TOWER_HEIGHT: usize> Tower<TOWER_HEIGHT> {
         tower
     }
 
-    fn map(self, f: impl FnMut(Option<Ring>) -> Option<Ring>) -> Self {
-        Self {
-            rings: self.rings.map(f),
-        }
-    }
-
     fn burried_score(&self) -> usize {
         let mut ring_type = None;
         let mut same_ring_type_score = 0;
@@ -286,13 +280,6 @@ impl<const TOWER_HEIGHT: usize> Game<TOWER_HEIGHT> {
                     continue;
                 }
 
-                let rings = self.towers[from_tower].rings;
-                if rings[1..].iter().all(|i| i == &rings[0])
-                    && self.towers[to_tower].rings[0].is_none()
-                {
-                    continue;
-                }
-
                 let m = Move::new(from_tower, to_tower);
                 if self.try_make_move(m, true).is_ok() {
                     res.push(m);
@@ -325,81 +312,18 @@ impl<const TOWER_HEIGHT: usize> Game<TOWER_HEIGHT> {
             }
         }
 
-        fn tower_solved<const TOWER_HEIGHT: usize>(tower: &Tower<TOWER_HEIGHT>) -> bool {
-            tower
-                .rings
-                .iter()
-                .all(|x| x.is_some() && x == &tower.rings[0])
-        }
-
-        let hash_state = |towers: &[Tower<TOWER_HEIGHT>]| {
+        let hash_state = |s: &[Tower<TOWER_HEIGHT>]| {
             let mut hasher = DefaultHasher::default();
 
-            let num_finished_towers = towers.iter().filter(|i| tower_solved(*i)).count();
-
-            num_finished_towers.hash(&mut hasher);
-            let mut filtered_towers = towers
-                .iter()
-                .filter(|i| !tower_solved(i) && i.height() != 0)
-                .enumerate()
-                .collect::<Vec<_>>();
-
-            filtered_towers.sort_by_cached_key(|(index, tower)| {
-                let mut rings = [0; TOWER_HEIGHT];
-
-                let mut count = 0;
-                for (idx, ring) in tower.rings.iter().copied().enumerate() {
-                    let Some(ring) = ring else { break };
-
-                    if rings[idx] == 0 {
-                        count += 1;
-                        for (j, ring2) in tower.rings[idx..].iter().copied().enumerate() {
-                            if ring2 == Some(ring) {
-                                rings[j] = count;
-                            }
-                        }
-                    }
-                }
-                (rings, *index)
-            });
-
-            let mut color_assignment = [None::<Ring>; 100];
-            let mut num_seen = 0;
-            let relabelled_towers = filtered_towers.iter().map(|(_, x)| x).map(|tower| {
-                tower.map(|ring| {
-                    ring.map(|ring| {
-                        *color_assignment[ring.0.get()].get_or_insert_with(|| {
-                            num_seen += 1;
-                            let ring = Ring(NonZero::new(num_seen).unwrap());
-                            ring
-                        })
-                    })
-                })
-            });
-
-            for x in relabelled_towers.into_iter().enumerate() {
+            for x in s.iter().filter(|i| i.height() != 0).enumerate() {
                 x.hash(&mut hasher);
             }
 
             hasher.finish()
         };
 
-        #[derive(PartialEq)]
-        struct Ordf32(f32);
-        impl Eq for Ordf32 {}
-        impl PartialOrd for Ordf32 {
-            fn partial_cmp(&self, other: &Self) -> Option<std::cmp::Ordering> {
-                Some(self.cmp(other))
-            }
-        }
-        impl Ord for Ordf32 {
-            fn cmp(&self, other: &Self) -> std::cmp::Ordering {
-                self.0.total_cmp(&other.0)
-            }
-        }
-
         let mut states = Vec::new();
-        let mut todo = BinaryHeap::<(Ordf32, usize, usize)>::new();
+        let mut todo = BinaryHeap::<((i64, i64), i64, usize)>::new();
         let mut had = HashSet::new();
         let mut ctr = 0;
 
@@ -408,7 +332,7 @@ impl<const TOWER_HEIGHT: usize> Game<TOWER_HEIGHT> {
             parent_index: 0,
             m: Move::new(0, 0),
         });
-        todo.push((Ordf32(0.0), 1000000000, 0));
+        todo.push(((0, 0), 1000000000, 0));
 
         while let Some((score, depth, state_index)) = todo.pop() {
             ctr += 1;
@@ -449,8 +373,36 @@ impl<const TOWER_HEIGHT: usize> Game<TOWER_HEIGHT> {
                 working_instance.towers = state.towers.clone();
                 working_instance.make_move(m).unwrap();
 
-                let num_solved = working_instance.num_solved();
-                let brs = working_instance.burried_ring_score();
+                let brs: i64 = {
+                    let this = &working_instance;
+                    let mut seen_bottom_rings = HashSet::new();
+                    this.towers
+                        .iter()
+                        .map(|i| {
+                            let this = &i;
+                            let mut ring_type = None;
+                            let mut burried_score = 0;
+
+                            for ring in this.rings.iter().rev().flatten() {
+                                if let Some(existing_ring_type) = ring_type
+                                    && existing_ring_type != *ring
+                                {
+                                    burried_score += 1;
+                                }
+                                ring_type = Some(*ring);
+                            }
+                            if let Some(Some(ring)) = this.rings.last() {
+                                if seen_bottom_rings.contains(ring) {
+                                    burried_score += 1;
+                                } else {
+                                    seen_bottom_rings.insert(ring);
+                                }
+                            }
+
+                            burried_score
+                        })
+                        .sum()
+                };
 
                 let new_state_hash = hash_state(&working_instance.towers);
                 if had.contains(&new_state_hash) {
@@ -464,9 +416,8 @@ impl<const TOWER_HEIGHT: usize> Game<TOWER_HEIGHT> {
                     m,
                 });
 
-                let score = (num_solved as f32 * 10.0) + (-(brs as f32) * 100.0);
-
-                todo.push((Ordf32(score), depth - 1, new_state_index));
+                let score = (depth) - (brs);
+                todo.push(((score, -depth), depth - 1, new_state_index));
             }
         }
 
@@ -824,7 +775,7 @@ fn main() -> io::Result<()> {
 
     let mut g = GameGenerator {
         num_extra_towers: 2,
-        num_ring_types: 16,
+        num_ring_types: 13,
     }
     .highest_burried_score::<4>(&seed);