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use crate::instance::Instance;
use crate::solution::{
RouteInfo, Solution, best_pair_insertion_with_info, build_route_with_pair,
build_route_with_pair_buf, compute_all_infos, route_distance,
};
/// Inter-route 2-pair relocate with threshold acceptance and split-destination support.
///
/// Removes 2 pairs from one route and inserts them into other routes.
/// Supports two modes:
/// - **Same-dst**: both pairs into one destination route (original behavior)
/// - **Split-dst**: each pair into a different destination route
///
/// `max_worsening` controls acceptance:
/// - 0.0 → only strictly improving moves (original behavior)
/// - >0.0 → accept moves that worsen distance by up to this amount
///
/// Returns true if a move was applied.
#[allow(clippy::too_many_lines)]
pub fn shake_inter_route_2pair(inst: &Instance, sol: &mut Solution, max_worsening: f64) -> bool {
let nr = sol.routes.len();
if nr < 2 {
return false;
}
let mut infos: Vec<RouteInfo> = Vec::new();
compute_all_infos(inst, &sol.routes, &mut infos);
// Best move tracking — accepts up to max_worsening increase
let mut best_delta = max_worsening;
// Move type: 0=none, 1=same-dst, 2=split-dst
let mut move_type: u8 = 0;
let mut mv_src: usize = 0;
let mut mv_p1: usize = 0;
let mut mv_p2: usize = 0;
// Same-dst fields
let mut mv_same_dst: usize = 0;
let mut mv_same_first_is_p1: bool = true;
let mut mv_same_ep1: usize = 0;
let mut mv_same_ed1: usize = 0;
let mut mv_same_ep2: usize = 0;
let mut mv_same_ed2: usize = 0;
// Split-dst fields
let mut mv_split_dst1: usize = 0;
let mut mv_split_ep1: usize = 0;
let mut mv_split_ed1: usize = 0;
let mut mv_split_dst2: usize = 0;
let mut mv_split_ep2: usize = 0;
let mut mv_split_ed2: usize = 0;
// Work buffers
let mut stripped_buf: Vec<usize> = Vec::new();
let mut intermediate_buf: Vec<usize> = Vec::new();
let mut info_intermediate = RouteInfo::new();
let mut pos_in_route: Vec<usize> = vec![usize::MAX; inst.n + 1];
let mut pos_touched: Vec<usize> = Vec::new();
for ri in 0..nr {
let route = &sol.routes[ri];
pos_touched.clear();
for (idx, &v) in route.iter().enumerate() {
pos_in_route[v] = idx;
pos_touched.push(v);
}
// Collect pickups in this route with their detour costs
let mut pairs: Vec<(f64, usize)> = Vec::new();
for idx in 1..route.len() - 1 {
let v = route[idx];
if !inst.is_pickup(v) {
continue;
}
let d = inst.delivery_of(v);
let pos_d = pos_in_route[d];
if pos_d == usize::MAX {
continue;
}
let prev_v = route[idx - 1];
let next_v = route[idx + 1];
let cost_v = inst.dist(prev_v, v) + inst.dist(v, next_v) - inst.dist(prev_v, next_v);
let prev_d = route[pos_d - 1];
let next_d = route[pos_d + 1];
let cost_d = inst.dist(prev_d, d) + inst.dist(d, next_d) - inst.dist(prev_d, next_d);
pairs.push((cost_v + cost_d, v));
}
if pairs.len() < 2 {
while let Some(v) = pos_touched.pop() {
pos_in_route[v] = usize::MAX;
}
continue;
}
// Select top-W worst-fitting pairs (W=8 for broader exploration)
let w = pairs.len().min(8);
pairs.sort_unstable_by(|a, b| b.0.partial_cmp(&a.0).unwrap());
pairs.truncate(w);
// Try all combinations of 2 from these W pairs
for i in 0..pairs.len() {
let p1 = pairs[i].1;
let d1 = inst.delivery_of(p1);
for &(_, p2) in &pairs[i + 1..] {
let d2 = inst.delivery_of(p2);
// Remove both pairs from source route
stripped_buf.clear();
for &v in route {
if v != p1 && v != d1 && v != p2 && v != d2 {
stripped_buf.push(v);
}
}
if stripped_buf.len() < 2 {
continue;
}
let delta_remove = route_distance(inst, &stripped_buf) - infos[ri].distance;
// For split-dst: track top-2 independent insertions for each pair.
// top[0] = best, top[1] = second-best (for when best routes collide).
// Each entry: (route_idx, delta_dist, ep, ed)
const NONE: (usize, f64, usize, usize) = (usize::MAX, f64::MAX, 0, 0);
let mut p1_top = [NONE; 2];
let mut p2_top = [NONE; 2];
for (rj, info_rj) in infos.iter().enumerate() {
if rj == ri {
continue;
}
// Compute insertion for each pair once, reuse for both same-dst and split-dst
let ins_p1 = best_pair_insertion_with_info::<false>(
inst,
&sol.routes[rj],
info_rj,
p1,
d1,
);
let ins_p2 = best_pair_insertion_with_info::<false>(
inst,
&sol.routes[rj],
info_rj,
p2,
d2,
);
// Update split-dst top-2 for p1
if let Some((new_dist, ep, ed)) = ins_p1 {
let delta = new_dist - info_rj.distance;
if delta < p1_top[0].1 {
p1_top[1] = p1_top[0];
p1_top[0] = (rj, delta, ep, ed);
} else if delta < p1_top[1].1 {
p1_top[1] = (rj, delta, ep, ed);
}
}
// Update split-dst top-2 for p2
if let Some((new_dist, ep, ed)) = ins_p2 {
let delta = new_dist - info_rj.distance;
if delta < p2_top[0].1 {
p2_top[1] = p2_top[0];
p2_top[0] = (rj, delta, ep, ed);
} else if delta < p2_top[1].1 {
p2_top[1] = (rj, delta, ep, ed);
}
}
// Same-dst: order A (p1 first, then p2)
if let Some((_dist_p1, ep1, ed1)) = ins_p1 {
build_route_with_pair_buf(
&sol.routes[rj],
p1,
ep1,
d1,
ed1,
&mut intermediate_buf,
);
info_intermediate.compute(inst, &intermediate_buf);
if let Some((dist_both, ep2, ed2)) = best_pair_insertion_with_info::<false>(
inst,
&intermediate_buf,
&info_intermediate,
p2,
d2,
) {
let total_delta = delta_remove + dist_both - info_rj.distance;
if total_delta < best_delta {
best_delta = total_delta;
move_type = 1;
mv_src = ri;
mv_p1 = p1;
mv_p2 = p2;
mv_same_dst = rj;
mv_same_first_is_p1 = true;
mv_same_ep1 = ep1;
mv_same_ed1 = ed1;
mv_same_ep2 = ep2;
mv_same_ed2 = ed2;
}
}
}
// Same-dst: order B (p2 first, then p1)
if let Some((_dist_p2, ep2, ed2)) = ins_p2 {
build_route_with_pair_buf(
&sol.routes[rj],
p2,
ep2,
d2,
ed2,
&mut intermediate_buf,
);
info_intermediate.compute(inst, &intermediate_buf);
if let Some((dist_both, ep1, ed1)) = best_pair_insertion_with_info::<false>(
inst,
&intermediate_buf,
&info_intermediate,
p1,
d1,
) {
let total_delta = delta_remove + dist_both - info_rj.distance;
if total_delta < best_delta {
best_delta = total_delta;
move_type = 1;
mv_src = ri;
mv_p1 = p1;
mv_p2 = p2;
mv_same_dst = rj;
mv_same_first_is_p1 = false;
mv_same_ep1 = ep2;
mv_same_ed1 = ed2;
mv_same_ep2 = ep1;
mv_same_ed2 = ed1;
}
}
}
}
// Evaluate best split-dst assignment (p1→dst1, p2→dst2, dst1 ≠ dst2)
if p1_top[0].0 != usize::MAX && p2_top[0].0 != usize::MAX {
let (split_p1, split_p2) = if p1_top[0].0 != p2_top[0].0 {
// Best routes differ — use both bests
(p1_top[0], p2_top[0])
} else {
// Same best route — try second-best for each, pick cheaper
let opt_a = if p1_top[1].0 != usize::MAX {
p1_top[1].1 + p2_top[0].1
} else {
f64::MAX
};
let opt_b = if p2_top[1].0 != usize::MAX {
p1_top[0].1 + p2_top[1].1
} else {
f64::MAX
};
if opt_a <= opt_b {
(p1_top[1], p2_top[0])
} else {
(p1_top[0], p2_top[1])
}
};
if split_p1.0 != usize::MAX && split_p2.0 != usize::MAX {
let total_delta = delta_remove + split_p1.1 + split_p2.1;
if total_delta < best_delta {
best_delta = total_delta;
move_type = 2;
mv_src = ri;
mv_p1 = p1;
mv_p2 = p2;
mv_split_dst1 = split_p1.0;
mv_split_ep1 = split_p1.2;
mv_split_ed1 = split_p1.3;
mv_split_dst2 = split_p2.0;
mv_split_ep2 = split_p2.2;
mv_split_ed2 = split_p2.3;
}
}
}
}
}
while let Some(v) = pos_touched.pop() {
pos_in_route[v] = usize::MAX;
}
}
// Apply the best move found
match move_type {
0 => false,
1 => {
// Same-dst: both pairs into one destination route
let d1 = inst.delivery_of(mv_p1);
let d2 = inst.delivery_of(mv_p2);
let (first_p, first_d, second_p, second_d) = if mv_same_first_is_p1 {
(mv_p1, d1, mv_p2, d2)
} else {
(mv_p2, d2, mv_p1, d1)
};
// Remove both pairs from source
stripped_buf.clear();
for &v in &sol.routes[mv_src] {
if v != mv_p1 && v != d1 && v != mv_p2 && v != d2 {
stripped_buf.push(v);
}
}
// Insert first pair into destination
build_route_with_pair_buf(
&sol.routes[mv_same_dst],
first_p,
mv_same_ep1,
first_d,
mv_same_ed1,
&mut intermediate_buf,
);
// Insert second pair
sol.routes[mv_same_dst] = build_route_with_pair(
&intermediate_buf,
second_p,
mv_same_ep2,
second_d,
mv_same_ed2,
);
// Update source route
if stripped_buf.len() <= 2 {
sol.routes.remove(mv_src);
} else {
sol.routes[mv_src].clone_from(&stripped_buf);
}
sol.routes.retain(|r| r.len() > 2);
true
}
2 => {
// Split-dst: p1 → dst1, p2 → dst2 (dst1 ≠ dst2 ≠ src)
let d1 = inst.delivery_of(mv_p1);
let d2 = inst.delivery_of(mv_p2);
// Remove both pairs from source
stripped_buf.clear();
for &v in &sol.routes[mv_src] {
if v != mv_p1 && v != d1 && v != mv_p2 && v != d2 {
stripped_buf.push(v);
}
}
// Insert p1 into dst1 (independent of dst2)
sol.routes[mv_split_dst1] = build_route_with_pair(
&sol.routes[mv_split_dst1],
mv_p1,
mv_split_ep1,
d1,
mv_split_ed1,
);
// Insert p2 into dst2 (independent of dst1)
sol.routes[mv_split_dst2] = build_route_with_pair(
&sol.routes[mv_split_dst2],
mv_p2,
mv_split_ep2,
d2,
mv_split_ed2,
);
// Update source route
if stripped_buf.len() <= 2 {
sol.routes.remove(mv_src);
} else {
sol.routes[mv_src].clone_from(&stripped_buf);
}
sol.routes.retain(|r| r.len() > 2);
true
}
_ => unreachable!(),
}
}