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priorityqueue.go
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priorityqueue.go
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// Very closely resembles the content of
// https://golang.org/pkg/container/heap/#example__priorityQueue
// Why am i copy-pasting parts of the documentation you ask?
// Well, this is the idiomatic way of doing it. Thanks for reading my rant.
package dapcstp
import (
"container/heap"
)
// An Item is something we manage in a priority queue.
type Item struct {
value int // The value of the item; node or arc index in our usage.
priority Value // The priority of the item in the queue.
// The index is needed by update and is maintained by the heap.Interface methods.
index int // The index of the item in the heap.
}
type priorityQueue []*Item
// A PriorityQueue implements heap.Interface and holds Items. Returns lowest priorirty first.
type PriorityQueue struct {
q priorityQueue
}
func (pq priorityQueue) Len() int { return len(pq) }
func (pq priorityQueue) Less(i, j int) bool {
return pq[i].priority < pq[j].priority
}
func (pq priorityQueue) Swap(i, j int) {
pq[i], pq[j] = pq[j], pq[i]
pq[i].index = i
pq[j].index = j
}
func (pq *priorityQueue) Push(x interface{}) {
n := len(*pq)
item := x.(*Item)
item.index = n
*pq = append(*pq, item)
}
func (pq *priorityQueue) Pop() interface{} {
old := *pq
n := len(old)
item := old[n-1]
item.index = -1 // for safety
*pq = old[0 : n-1]
return item
}
func (pq *PriorityQueue) Pop() *Item {
return heap.Pop(&pq.q).(*Item)
}
func (pq *PriorityQueue) Push(x *Item) {
heap.Push(&pq.q, x)
}
func (pq *PriorityQueue) Len() int {
return pq.q.Len()
}
// Update modifies the priority and value of an Item in the queue.
func (pq *PriorityQueue) Update(item *Item, value int, priority Value) {
item.value = value
item.priority = priority
heap.Fix(&pq.q, item.index)
}