solverforge_solver/heuristic/selector/

sublist_swap.rs

/* Sublist swap move selector for segment exchange.

Generates `SublistSwapMove`s that swap contiguous segments within or between
list variables. Useful for balanced inter-route segment exchanges in VRP.

# Complexity

For n entities with average route length m and max segment size k:
- Intra-entity pairs: O(n * m² * k²) — triangular over non-overlapping segments
- Inter-entity pairs: O(n² * m² * k²) — all pairs across entities

Use a forager that quits early for large instances.

# Example

```
use solverforge_solver::heuristic::selector::sublist_swap::SublistSwapMoveSelector;
use solverforge_solver::heuristic::selector::entity::FromSolutionEntitySelector;
use solverforge_solver::heuristic::selector::MoveSelector;
use solverforge_core::domain::PlanningSolution;
use solverforge_core::score::SoftScore;

#[derive(Clone, Debug)]
struct Vehicle { visits: Vec<i32> }

#[derive(Clone, Debug)]
struct Solution { vehicles: Vec<Vehicle>, score: Option<SoftScore> }

impl PlanningSolution for Solution {
type Score = SoftScore;
fn score(&self) -> Option<Self::Score> { self.score }
fn set_score(&mut self, score: Option<Self::Score>) { self.score = score; }
}

fn list_len(s: &Solution, entity_idx: usize) -> usize {
s.vehicles.get(entity_idx).map_or(0, |v| v.visits.len())
}
fn sublist_remove(s: &mut Solution, entity_idx: usize, start: usize, end: usize) -> Vec<i32> {
s.vehicles.get_mut(entity_idx)
.map(|v| v.visits.drain(start..end).collect())
.unwrap_or_default()
}
fn sublist_insert(s: &mut Solution, entity_idx: usize, pos: usize, items: Vec<i32>) {
if let Some(v) = s.vehicles.get_mut(entity_idx) {
for (i, item) in items.into_iter().enumerate() {
v.visits.insert(pos + i, item);
}
}
}

// Swap segments of size 1..=3 between routes
let selector = SublistSwapMoveSelector::<Solution, i32, _>::new(
FromSolutionEntitySelector::new(0),
1, 3,
list_len,
sublist_remove,
sublist_insert,
"visits",
0,
);
```
*/

use std::fmt::Debug;
use std::marker::PhantomData;

use solverforge_core::domain::PlanningSolution;
use solverforge_scoring::Director;

use crate::heuristic::r#move::SublistSwapMove;

use super::entity::EntitySelector;
use super::list_support::collect_selected_entities;
use super::move_selector::{ArenaMoveCursor, MoveSelector};
use super::sublist_support::{count_intra_sublist_swap_moves_for_len, count_sublist_segments};

/// A move selector that generates sublist swap moves.
///
/// For each pair of segments (which may span different entities), generates
/// a swap move. Intra-entity swaps require non-overlapping segments.
///
/// # Type Parameters
/// * `S` - The solution type
/// * `V` - The list element type
/// * `ES` - The entity selector type
pub struct SublistSwapMoveSelector<S, V, ES> {
    entity_selector: ES,
    // Minimum segment size (inclusive).
    min_sublist_size: usize,
    // Maximum segment size (inclusive).
    max_sublist_size: usize,
    list_len: fn(&S, usize) -> usize,
    list_get: fn(&S, usize, usize) -> Option<V>,
    sublist_remove: fn(&mut S, usize, usize, usize) -> Vec<V>,
    sublist_insert: fn(&mut S, usize, usize, Vec<V>),
    variable_name: &'static str,
    descriptor_index: usize,
    _phantom: PhantomData<(fn() -> S, fn() -> V)>,
}

impl<S, V: Debug, ES: Debug> Debug for SublistSwapMoveSelector<S, V, ES> {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.debug_struct("SublistSwapMoveSelector")
            .field("entity_selector", &self.entity_selector)
            .field("min_sublist_size", &self.min_sublist_size)
            .field("max_sublist_size", &self.max_sublist_size)
            .field("variable_name", &self.variable_name)
            .field("descriptor_index", &self.descriptor_index)
            .finish()
    }
}

impl<S, V, ES> SublistSwapMoveSelector<S, V, ES> {
    /* Creates a new sublist swap move selector.

    # Arguments
    * `entity_selector` - Selects entities to consider for swaps
    * `min_sublist_size` - Minimum segment length (must be ≥ 1)
    * `max_sublist_size` - Maximum segment length
    * `list_len` - Function to get list length for an entity
    * `sublist_remove` - Function to drain range `[start, end)`, returning elements
    * `sublist_insert` - Function to insert elements at a position
    * `variable_name` - Name of the list variable
    * `descriptor_index` - Entity descriptor index

    # Panics
    Panics if `min_sublist_size == 0` or `max_sublist_size < min_sublist_size`.
    */
    #[allow(clippy::too_many_arguments)]
    pub fn new(
        entity_selector: ES,
        min_sublist_size: usize,
        max_sublist_size: usize,
        list_len: fn(&S, usize) -> usize,
        list_get: fn(&S, usize, usize) -> Option<V>,
        sublist_remove: fn(&mut S, usize, usize, usize) -> Vec<V>,
        sublist_insert: fn(&mut S, usize, usize, Vec<V>),
        variable_name: &'static str,
        descriptor_index: usize,
    ) -> Self {
        assert!(min_sublist_size >= 1, "min_sublist_size must be at least 1");
        assert!(
            max_sublist_size >= min_sublist_size,
            "max_sublist_size must be >= min_sublist_size"
        );
        Self {
            entity_selector,
            min_sublist_size,
            max_sublist_size,
            list_len,
            list_get,
            sublist_remove,
            sublist_insert,
            variable_name,
            descriptor_index,
            _phantom: PhantomData,
        }
    }
}

impl<S, V, ES> MoveSelector<S, SublistSwapMove<S, V>> for SublistSwapMoveSelector<S, V, ES>
where
    S: PlanningSolution,
    V: Clone + PartialEq + Send + Sync + Debug + 'static,
    ES: EntitySelector<S>,
{
    type Cursor<'a>
        = ArenaMoveCursor<S, SublistSwapMove<S, V>>
    where
        Self: 'a;

    fn open_cursor<'a, D: Director<S>>(&'a self, score_director: &D) -> Self::Cursor<'a> {
        let list_len = self.list_len;
        let sublist_remove = self.sublist_remove;
        let sublist_insert = self.sublist_insert;
        let variable_name = self.variable_name;
        let descriptor_index = self.descriptor_index;
        let min_seg = self.min_sublist_size;
        let max_seg = self.max_sublist_size;

        let selected = collect_selected_entities(&self.entity_selector, score_director, list_len);
        let entities = selected.entities;
        let route_lens = selected.route_lens;
        let mut moves = Vec::new();
        let list_get = self.list_get;

        for (i, &entity_a) in entities.iter().enumerate() {
            let len_a = route_lens[i];

            for first_start in 0..len_a {
                for first_size in min_seg..=max_seg {
                    let first_end = first_start + first_size;
                    if first_end > len_a {
                        break;
                    }

                    for second_start in first_end..len_a {
                        for second_size in min_seg..=max_seg {
                            let second_end = second_start + second_size;
                            if second_end > len_a {
                                break;
                            }
                            moves.push(SublistSwapMove::new(
                                entity_a,
                                first_start,
                                first_end,
                                entity_a,
                                second_start,
                                second_end,
                                list_len,
                                list_get,
                                sublist_remove,
                                sublist_insert,
                                variable_name,
                                descriptor_index,
                            ));
                        }
                    }
                }
            }

            for (j, &entity_b) in entities.iter().enumerate() {
                if j <= i {
                    continue;
                }
                let len_b = route_lens[j];
                if len_b == 0 {
                    continue;
                }

                for first_start in 0..len_a {
                    for first_size in min_seg..=max_seg {
                        let first_end = first_start + first_size;
                        if first_end > len_a {
                            break;
                        }

                        for second_start in 0..len_b {
                            for second_size in min_seg..=max_seg {
                                let second_end = second_start + second_size;
                                if second_end > len_b {
                                    break;
                                }
                                moves.push(SublistSwapMove::new(
                                    entity_a,
                                    first_start,
                                    first_end,
                                    entity_b,
                                    second_start,
                                    second_end,
                                    list_len,
                                    list_get,
                                    sublist_remove,
                                    sublist_insert,
                                    variable_name,
                                    descriptor_index,
                                ));
                            }
                        }
                    }
                }
            }
        }

        ArenaMoveCursor::from_moves(moves)
    }

    fn size<D: Director<S>>(&self, score_director: &D) -> usize {
        let selected =
            collect_selected_entities(&self.entity_selector, score_director, self.list_len);
        let segment_counts: Vec<usize> = selected
            .route_lens
            .iter()
            .map(|&route_len| {
                count_sublist_segments(route_len, self.min_sublist_size, self.max_sublist_size)
            })
            .collect();
        let intra: usize = selected
            .route_lens
            .iter()
            .map(|&route_len| {
                count_intra_sublist_swap_moves_for_len(
                    route_len,
                    self.min_sublist_size,
                    self.max_sublist_size,
                )
            })
            .sum();
        let inter: usize = (0..selected.route_lens.len())
            .flat_map(|left| (left + 1..selected.route_lens.len()).map(move |right| (left, right)))
            .map(|(left, right)| segment_counts[left] * segment_counts[right])
            .sum();
        intra + inter
    }
}