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perf: reduce allocations in pathfinding hot paths #720

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9c5e5c0
perf: pre-allocate HashMap in separate_components
Copilot Nov 5, 2025
e1c0582
perf: pre-allocate BinaryHeap in A* and HashMap in components
Copilot Nov 5, 2025
6aafd93
perf: pre-allocate BinaryHeap in astar_bag
Copilot Nov 5, 2025
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6 changes: 4 additions & 2 deletions src/directed/astar.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -92,7 +92,8 @@ where
FH: FnMut(&N) -> C,
FS: FnMut(&N) -> bool,
{
let mut to_see = BinaryHeap::new();
// Pre-allocate heap with a reasonable default capacity to reduce reallocations
let mut to_see = BinaryHeap::with_capacity(64);
to_see.push(SmallestCostHolder {
estimated_cost: Zero::zero(),
cost: Zero::zero(),
Expand Down Expand Up @@ -184,7 +185,8 @@ where
FH: FnMut(&N) -> C,
FS: FnMut(&N) -> bool,
{
let mut to_see = BinaryHeap::new();
// Pre-allocate heap with a reasonable default capacity to reduce reallocations
let mut to_see = BinaryHeap::with_capacity(64);
let mut min_cost = None;
let mut sinks = HashSet::new();
to_see.push(SmallestCostHolder {
Expand Down
11 changes: 8 additions & 3 deletions src/undirected/connected_components.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -5,7 +5,7 @@ use std::collections::{HashMap, HashSet};
use std::hash::Hash;
use std::marker::PhantomData;

use rustc_hash::{FxHashMap, FxHashSet};
use rustc_hash::{FxBuildHasher, FxHashMap, FxHashSet};

/// A connected component implementation for various generic types.
///
Expand Down Expand Up @@ -60,7 +60,9 @@ where
#[must_use]
pub fn separate_components(groups: &[It]) -> (HashMap<&N, usize>, Vec<usize>) {
let mut table = (0..groups.len()).collect::<Vec<_>>();
let mut indices = HashMap::new();
// Pre-size the hash map to reduce reallocations
let estimated_capacity = groups.iter().map(|g| g.into_iter().count()).sum();
let mut indices = HashMap::with_capacity(estimated_capacity);
for (mut group_index, group) in groups.iter().enumerate() {
let mut is_empty = true;
for element in group {
Expand Down Expand Up @@ -103,7 +105,10 @@ where
#[must_use]
pub fn components(groups: &[It]) -> C2 {
let (_, gindices) = Self::separate_components(groups);
let mut gb: FxHashMap<usize, FxHashSet<N>> = FxHashMap::default();
// Pre-size the hash map to reduce reallocations
let estimated_capacity = gindices.iter().filter(|&&n| n != usize::MAX).count();
let mut gb: FxHashMap<usize, FxHashSet<N>> =
FxHashMap::with_capacity_and_hasher(estimated_capacity, FxBuildHasher);
for (i, n) in gindices
.into_iter()
.enumerate()
Expand Down
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