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-// Copyright 2012 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-// This example demonstrates a priority queue built using the heap interface.
-package heap_test
-
-import (
- "container/heap"
- "fmt"
-)
-
-// An Item is something we manage in a priority queue.
-type Item struct {
- value string // The value of the item; arbitrary.
- priority int // The priority of the item in the queue.
- // The index is needed by changePriority and is maintained by the heap.Interface methods.
- index int // The index of the item in the heap.
-}
-
-// A PriorityQueue implements heap.Interface and holds Items.
-type PriorityQueue []*Item
-
-func (pq PriorityQueue) Len() int { return len(pq) }
-
-func (pq PriorityQueue) Less(i, j int) bool {
- // We want Pop to give us the highest, not lowest, priority so we use greater than here.
- 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{}) {
- // Push and Pop use pointer receivers because they modify the slice's length,
- // not just its contents.
- n := len(*pq)
- item := x.(*Item)
- item.index = n
- *pq = append(*pq, item)
-}
-
-func (pq *PriorityQueue) Pop() interface{} {
- a := *pq
- n := len(a)
- item := a[n-1]
- item.index = -1 // for safety
- *pq = a[0 : n-1]
- return item
-}
-
-// update is not used by the example but shows how to take the top item from
-// the queue, update its priority and value, and put it back.
-func (pq *PriorityQueue) update(value string, priority int) {
- item := heap.Pop(pq).(*Item)
- item.value = value
- item.priority = priority
- heap.Push(pq, item)
-}
-
-// changePriority is not used by the example but shows how to change the
-// priority of an arbitrary item.
-func (pq *PriorityQueue) changePriority(item *Item, priority int) {
- heap.Remove(pq, item.index)
- item.priority = priority
- heap.Push(pq, item)
-}
-
-// This example pushes 10 items into a PriorityQueue and takes them out in
-// order of priority.
-func Example() {
- const nItem = 10
- // Random priorities for the items (a permutation of 0..9, times 11)).
- priorities := [nItem]int{
- 77, 22, 44, 55, 11, 88, 33, 99, 00, 66,
- }
- values := [nItem]string{
- "zero", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine",
- }
- // Create a priority queue and put some items in it.
- pq := make(PriorityQueue, 0, nItem)
- for i := 0; i < cap(pq); i++ {
- item := &Item{
- value: values[i],
- priority: priorities[i],
- }
- heap.Push(&pq, item)
- }
- // Take the items out; should arrive in decreasing priority order.
- // For example, the highest priority (99) is the seventh item, so output starts with 99:"seven".
- for i := 0; i < nItem; i++ {
- item := heap.Pop(&pq).(*Item)
- fmt.Printf("%.2d:%s ", item.priority, item.value)
- }
- // Output:
- // 99:seven 88:five 77:zero 66:nine 55:three 44:two 33:six 22:one 11:four 00:eight
-}