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