PriorityQueue

This crate implements a Priority Queue with a function to change the priority of an object. Priority and items are stored in an IndexMap and the queue is implemented as a Heap of indexes.

Please read the API documentation here

Usage

To use this crate, simply add the following string to your Cargo.toml:

priority-queue = "0.7.0"

Version numbers follow the semver convention.

Then use the data structure inside your Rust source code as in the following Example.

Remember that, if you need serde support, you should compile using --features serde.

Example

extern crate priority_queue;

use priority_queue::PriorityQueue;

fn main() {
    let mut pq = PriorityQueue::new();

    assert!(pq.is_empty());
    pq.push("Apples", 5);
    pq.push("Bananas", 8);
    pq.push("Strawberries", 23);

    assert_eq!(pq.peek(), Some((&"Strawberries", &23)));

    for (item, _) in pq.into_sorted_iter() {
        println!("{}", item);
    }
}

Note: in recent versions of Rust (edition 2018) the extern crate priority_queue is not necessary anymore!

Speeding up

You can use custom BuildHasher for the underlying IndexMap and therefore achieve better performance. For example you can create the queue with the speedy FxHash hasher:

use hashbrown::hash_map::DefaultHashBuilder;

let mut pq = PriorityQueue::<_, _, DefaultHashBuilder>::with_default_hasher();

Attention: FxHash does not offer any protection for dos attacks. This means that some pathological inputs can make the operations on the hashmap O(n^2). Use the standard hasher if you cannot control the inputs.

Benchmarks

Some benchmarks have been run to compare the performances of this priority queue to the standard BinaryHeap, also using the FxHash hasher. The benchmarks produced the following results:

test benchmarks::push_and_pop                    ... bench:          80 ns/iter (+/- 6)
test benchmarks::push_and_pop_fx                 ... bench:          49 ns/iter (+/- 5)
test benchmarks::push_and_pop_on_large_queue     ... bench:         296 ns/iter (+/- 25)
test benchmarks::push_and_pop_on_large_queue_fx  ... bench:         259 ns/iter (+/- 41)
test benchmarks::push_and_pop_on_large_queue_std ... bench:          75 ns/iter (+/- 6)
test benchmarks::push_and_pop_std                ... bench:          11 ns/iter (+/- 1)

Contributing

Feel free to contribute to this project with pull requests and/or issues. All contribution should be under a license compatible with the GNU LGPL.

Changes

• 0.7.0 Implement the push_increase and push_decrease convenience methods.
• 0.6.0 Allow the usage of custom hasher
• 0.5.4 Prevent panic on extending an empty queue
• 0.5.3 New implementation of the Default trait avoids the requirement that P: Default
• 0.5.2 Fix documentation formatting
• 0.5.1 Add some documentation for iter_mut()
• 0.5.0 Fix #7 implementing the iter_mut features
• 0.4.5 Fix #6 for change_priority and change_priority_by
• 0.4.4 Fix #6
• 0.4.3 Fix #4 changing the way PriorityQueue serializes. Note that old serialized PriorityQueues may be incompatible with the new version. The API should not be changed instead.
• 0.4.2 Improved performance using some unsafe code in the implementation.
• 0.4.1 Support for serde when compiled with --features serde. serde marked as optional and serde-test as dev-dipendency. Now compiling the crate won't download and compile also serde-test, neither serde if not needed.
• 0.4.0 Support for serde when compiled with cfg(serde)
• 0.3.1 Fix #3
• 0.3.0 Implement PartialEq and Eq traits