Imported Upstream version 1.1~hg20130304upstream/1.1_hg20130304

1 files changed, 95 insertions, 0 deletions

diff --git a/src/pkg/container/heap/example_pq_test.go b/src/pkg/container/heap/example_pq_test.go
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index 000000000..8cbeb8d70
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+++ b/src/pkg/container/heap/example_pq_test.go
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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 update 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{}) {
+	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
+}
+
+// update modifies the priority and value of an Item in the queue.
+func (pq *PriorityQueue) update(item *Item, value string, priority int) {
+	heap.Remove(pq, item.index)
+	item.value = value
+	item.priority = priority
+	heap.Push(pq, item)
+}
+
+// This example inserts some items into a PriorityQueue, manipulates an item,
+// and then removes the items in priority order.
+func Example_priorityQueue() {
+	// Some items and their priorities.
+	items := map[string]int{
+		"banana": 3, "apple": 2, "pear": 4,
+	}
+
+	// Create a priority queue and put the items in it.
+	pq := &PriorityQueue{}
+	heap.Init(pq)
+	for value, priority := range items {
+		item := &Item{
+			value:    value,
+			priority: priority,
+		}
+		heap.Push(pq, item)
+	}
+
+	// Insert a new item and then modify its priority.
+	item := &Item{
+		value:    "orange",
+		priority: 1,
+	}
+	heap.Push(pq, item)
+	pq.update(item, item.value, 5)
+
+	// Take the items out; they arrive in decreasing priority order.
+	for pq.Len() > 0 {
+		item := heap.Pop(pq).(*Item)
+		fmt.Printf("%.2d:%s ", item.priority, item.value)
+	}
+	// Output:
+	// 05:orange 04:pear 03:banana 02:apple
+}