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priority_queue.go
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/
priority_queue.go
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package collection
import (
"errors"
"fmt"
)
var (
ErrEmptyPriorityQueue = errors.New("empty priority queue")
)
type WithPriority[T any] struct {
Item T
Priority float32
}
type priorityQueue[T any] []WithPriority[T]
func (pq priorityQueue[T]) Len() int { return len(pq) }
func (pq *priorityQueue[T]) Push(x WithPriority[T]) {
*pq = append(*pq, x)
pq.up(pq.Len() - 1)
}
func (pq *priorityQueue[T]) Pop() WithPriority[T] {
n := pq.Len() - 1
pq.swap(0, n)
pq.down(0, n)
item := (*pq)[n]
*pq = (*pq)[0:n]
return item
}
// derived from container/heap
func (pq priorityQueue[T]) init() {
// heapify
n := pq.Len()
for i := n/2 - 1; i >= 0; i-- {
pq.down(i, n)
}
}
func (pq priorityQueue[T]) less(i, j int) bool {
return pq[i].Priority < pq[j].Priority
}
func (pq priorityQueue[T]) swap(i, j int) {
pq[i], pq[j] = pq[j], pq[i]
}
// derived from container/heap
func (pq priorityQueue[T]) up(j int) {
for {
i := (j - 1) / 2 // parent
if i == j || !pq.less(j, i) {
break
}
pq.swap(i, j)
j = i
}
}
// derived from container/heap
func (pq priorityQueue[T]) down(i0, n int) bool {
i := i0
for {
j1 := 2*i + 1
if n <= j1 || j1 < 0 { // j1 < 0 after int overflow
break
}
j := pq.getLesserSibling(j1, n)
if !pq.less(j, i) {
break
}
pq.swap(i, j)
i = j
}
return i > i0
}
func (pq priorityQueue[T]) getLesserSibling(lIdx, n int) int {
ret := lIdx // left child
if rIdx := lIdx + 1; rIdx < n && pq.less(rIdx, lIdx) {
ret = rIdx // = 2*i + 2 // right child
}
return ret
}
type PriorityQueue[T any] struct {
priorityQueue[T]
}
func NewPriorityQueue[T any](capacity int) *PriorityQueue[T] {
return &PriorityQueue[T]{
priorityQueue: make(priorityQueue[T], 0, capacity),
}
}
func NewPriorityQueueFromSlice[T any](data []WithPriority[T]) *PriorityQueue[T] {
pq := priorityQueue[T](data)
pq.init()
return &PriorityQueue[T]{
priorityQueue: pq,
}
}
func (pq *PriorityQueue[T]) Push(item T, priority float32) {
pq.priorityQueue.Push(
WithPriority[T]{
Item: item,
Priority: priority,
},
)
}
func (pq *PriorityQueue[T]) PopWithPriority() (ret WithPriority[T], _ error) {
if pq.Len() == 0 {
return ret, ErrEmptyPriorityQueue
}
item := pq.priorityQueue.Pop()
return item, nil
}
func (pq *PriorityQueue[T]) Pop() (ret T, _ error) {
item, err := pq.PopWithPriority()
if err != nil {
return ret, err
}
return item.Item, nil
}
func (pq *PriorityQueue[T]) PeekWithPriority(n int) (ret WithPriority[T], _ error) {
if pq.priorityQueue.Len() <= n {
return ret, fmt.Errorf("index out of range: %d", n)
}
item := pq.priorityQueue[n]
return item, nil
}
func (pq *PriorityQueue[T]) Peek(n int) (ret T, _ error) {
item, err := pq.PeekWithPriority(n)
if err != nil {
return ret, err
}
return item.Item, nil
}
func (pq *PriorityQueue[T]) Len() int {
return pq.priorityQueue.Len()
}