queues/priorityqueue/priorityqueue.go

// Copyright (c) 2015, Emir Pasic. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// Package priorityqueue implements a priority queue backed by binary queue.
//
// An unbounded priority queue based on a priority queue.
// The elements of the priority queue are ordered by a comparator provided at queue construction time.
//
// The heap of this queue is the least/smallest element with respect to the specified ordering.
// If multiple elements are tied for least value, the heap is one of those elements arbitrarily.
//
// Structure is not thread safe.
//
// References: https://en.wikipedia.org/wiki/Priority_queue
package priorityqueue

import (
	"cmp"
	"fmt"
	"strings"

	"github.com/emirpasic/gods/v2/queues"
	"github.com/emirpasic/gods/v2/trees/binaryheap"
	"github.com/emirpasic/gods/v2/utils"
)

// Assert Queue implementation
var _ queues.Queue[int] = (*Queue[int])(nil)

// Queue holds elements in an array-list
type Queue[T comparable] struct {
	heap       *binaryheap.Heap[T]
	Comparator utils.Comparator[T]
}

func New[T cmp.Ordered]() *Queue[T] {
	return NewWith[T](cmp.Compare[T])
}

// NewWith instantiates a new empty queue with the custom comparator.
func NewWith[T comparable](comparator utils.Comparator[T]) *Queue[T] {
	return &Queue[T]{heap: binaryheap.NewWith(comparator), Comparator: comparator}
}

// Enqueue adds a value to the end of the queue
func (queue *Queue[T]) Enqueue(value T) {
	queue.heap.Push(value)
}

// Dequeue removes first element of the queue and returns it, or nil if queue is empty.
// Second return parameter is true, unless the queue was empty and there was nothing to dequeue.
func (queue *Queue[T]) Dequeue() (value T, ok bool) {
	return queue.heap.Pop()
}

// Peek returns top element on the queue without removing it, or nil if queue is empty.
// Second return parameter is true, unless the queue was empty and there was nothing to peek.
func (queue *Queue[T]) Peek() (value T, ok bool) {
	return queue.heap.Peek()
}

// Empty returns true if queue does not contain any elements.
func (queue *Queue[T]) Empty() bool {
	return queue.heap.Empty()
}

// Size returns number of elements within the queue.
func (queue *Queue[T]) Size() int {
	return queue.heap.Size()
}

// Clear removes all elements from the queue.
func (queue *Queue[T]) Clear() {
	queue.heap.Clear()
}

// Values returns all elements in the queue.
func (queue *Queue[T]) Values() []T {
	return queue.heap.Values()
}

// String returns a string representation of container
func (queue *Queue[T]) String() string {
	str := "PriorityQueue\n"
	values := make([]string, queue.heap.Size(), queue.heap.Size())
	for index, value := range queue.heap.Values() {
		values[index] = fmt.Sprintf("%v", value)
	}
	str += strings.Join(values, ", ")
	return str
}