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April 6, 2018 08:38
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using heap given by go library
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// This example demonstrates a priority queue built using the heap interface. | |
package main | |
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) { | |
item.value = value | |
item.priority = priority | |
heap.Fix(pq, item.index) | |
} | |
// This example creates a PriorityQueue with some items, adds and manipulates an item, | |
// and then removes the items in priority order. | |
func main() { | |
// Some items and their priorities. | |
items := map[string]int{ | |
"banana": 3, "apple": 2, "pear": 4, | |
} | |
// Create a priority queue, put the items in it, and | |
// establish the priority queue (heap) invariants. | |
pq := make(PriorityQueue, len(items)) | |
i := 0 | |
for value, priority := range items { | |
pq[i] = &Item{ | |
value: value, | |
priority: priority, | |
index: i, | |
} | |
i++ | |
} | |
heap.Init(&pq) | |
// 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) | |
} | |
} |
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