go 数据结构 – 优先队列（堆）
使用“container/heap”包，构建堆或者优先队列，需要自己定义Sort方法的内容及Push Pop方法。
//官方示例1 最小堆
// This example demonstrates an integer heap built using the heap interface.
package main
import (
"container/heap"
"fmt"
)
// An IntHeap is a min-heap of ints.
type IntHeap []int
func (h IntHeap) Len() int { return len(h) }
func (h IntHeap) Less(i, j int) bool { return h[i] < h[j] }
func (h IntHeap) Swap(i, j int) { h[i], h[j] = h[j], h[i] }
func (h *IntHeap) Push(x interface{}) {
// Push and Pop use pointer receivers because they modify the slice's length,
// not just its contents.
*h = append(*h, x.(int))
}
func (h *IntHeap) Pop() interface{} {
old := *h
n := len(old)
x := old[n-1]
*h = old[0 : n-1]
return x
}
// This example inserts several ints into an IntHeap, checks the minimum,
// and removes them in order of priority.
func main() {
h := &IntHeap{2, 1, 5}
heap.Init(h)
heap.Push(h, 3)
fmt.Printf("minimum: %d\n", (*h)[0])
for h.Len() > 0 {
fmt.Printf("%d ", heap.Pop(h))
}
}
//官方示例2 优先队列
// 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]
old[n-1] = nil // avoid memory leak
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)
}
}
//实际使用
import (
"container/heap"
"fmt"
)
type Item struct {
day int
apple int
}
type PriortyQueue []*Item
func (pq PriortyQueue) Len() int {return len(pq)}
func (pq PriortyQueue) Less(i, j int) bool {
return pq[i].day > pq[j].day
}
func (pq PriortyQueue) Swap(i, j int) {
pq[i], pq[j] = pq[j], pq[i]
}
func (pq *PriortyQueue) Push(x interface{}) {
item := x.(*Item)
*pq = append(*pq, item)
}
func (pq *PriortyQueue) Pop() interface{} {
old := *pq
n := len(old)
item := old[n-1]
old[n-1] = nil
*pq = old[0:n-1]
return item
}
func eatenApples(apples []int, days []int) int {
pq := make(PriortyQueue, 0)
n := len(apples)
res := 0
for i := 0; i <= 40000; i++ {
if i < n && apples[i] > 0 {
heap.Push(&pq, &Item{day: i+days[i]-1, apple: apples[i]})
}
for pq.Len() > 0 && pq[pq.Len()-1].day < i {
_ = pq.Pop()
}
if pq.Len() == 0 {continue}
x := pq.Pop().(*Item)
x.apple -= 1
res += 1
if x.apple > 0 {heap.Push(&pq, x)}
}
return res
}
//附Scala中优先队列使用
import scala.collection.mutable.PriorityQueue
object Solution {
def eatenApples(apples: Array[Int], days: Array[Int]): Int = {
val heap = PriorityQueue.empty[(Int, Int)](Ordering.by(n => n._1)).reverse
var res = 0
var n = apples.length
var i = 0
while (i < n || heap.length > 0){
//while (i < 10){
if (i < n && apples(i) > 0) {
heap.enqueue(((i + days(i) -1), apples(i)))
}
while (heap.length > 0 && heap.head._1 < i) {
var temp = heap.dequeue
}
if (heap.length > 0) {
var x = heap.dequeue
res += 1
if (x._2-1 > 0) {
heap.enqueue((x._1, x._2-1))
}
}
i += 1
}
return res
}
}