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//heap.Interface定义
type Interface interface {
	sort.Interface
	Push(x interface{}) // add x as element Len()
	Pop() interface{}   // remove and return element Len() - 1.
}

//sort.Interface定义
type Interface interface {
	// Len is the number of elements in the collection.
	Len() int
	// Less reports whether the element with
	// index i should sort before the element with index j.
	Less(i, j int) bool
	// Swap swaps the elements with indexes i and j.
	Swap(i, j int)
}

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type IntHeap []int // 定义一个类型

func (h IntHeap) Len() int { return len(h) } // 绑定len方法,返回长度
func (h IntHeap) Less(i, j int) bool { // 绑定less方法
	return h[i] < h[j] // 如果h[i]<h[j]生成的就是小根堆，如果h[i]>h[j]生成的就是大根堆
}
func (h IntHeap) Swap(i, j int) { // 绑定swap方法，交换两个元素位置
	h[i], h[j] = h[j], h[i]
}

func (h *IntHeap) Pop() interface{} { // 绑定pop方法，从最后拿出一个元素并返回
	old := *h
	n := len(old)
	x := old[n-1]
	*h = old[0 : n-1]
	return x
}

func (h *IntHeap) Push(x interface{}) { // 绑定push方法，插入新元素
	*h = append(*h, x.(int))
}

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// Copyright 2009 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.

// Package heap provides heap operations for any type that implements
// heap.Interface. A heap is a tree with the property that each node is the
// minimum-valued node in its subtree.
//
// The minimum element in the tree is the root, at index 0.
//
// A heap is a common way to implement a priority queue. To build a priority
// queue, implement the Heap interface with the (negative) priority as the
// ordering for the Less method, so Push adds items while Pop removes the
// highest-priority item from the queue. The Examples include such an
// implementation; the file example_pq_test.go has the complete source.
//
package heap

import "sort"

// The Interface type describes the requirements
// for a type using the routines in this package.
// Any type that implements it may be used as a
// min-heap with the following invariants (established after
// Init has been called or if the data is empty or sorted):
//
//	!h.Less(j, i) for 0 <= i < h.Len() and 2*i+1 <= j <= 2*i+2 and j < h.Len()
//
// Note that Push and Pop in this interface are for package heap's
// implementation to call. To add and remove things from the heap,
// use heap.Push and heap.Pop.
type Interface interface {
	sort.Interface
	Push(x interface{}) // add x as element Len()
	Pop() interface{}   // remove and return element Len() - 1.
}

// 初始化，调整一般数据就已经OK了
func Init(h Interface) {
	// heapify
	n := h.Len()
	for i := n/2 - 1; i >= 0; i-- {
		down(h, i, n)
	}
}

//把元素放在最后面，然后向上调整
func Push(h Interface, x interface{}) {
	h.Push(x)
	up(h, h.Len()-1)
}

//交换第一个和最后一个元素，然后从第一个元素开始向下调整，调整到n-1，然后弹出n-1的数据
func Pop(h Interface) interface{} {
	n := h.Len() - 1
	h.Swap(0, n)
	down(h, 0, n)
	return h.Pop()
}

// 移除下标i的数据，即把下标i和最后一个元素互换，然后调整
//先向下调整，如果不需要调整，则位置不变，即也不需要向上调整了，不然就需要向上调整了
func Remove(h Interface, i int) interface{} {
	n := h.Len() - 1
	if n != i {
		h.Swap(i, n)
		if !down(h, i, n) {
			up(h, i)
		}
	}
	return h.Pop()
}

// 下标i的调整逻辑
func Fix(h Interface, i int) {
	if !down(h, i, h.Len()) {
		up(h, i)
	}
}

//向上调整逻辑
func up(h Interface, j int) {
	for {
		i := (j - 1) / 2             // 父节点的下标
		if i == j || !h.Less(j, i) { //已经到顶了，或者不满足要求了，则跳出for循环
			break
		}
		h.Swap(i, j) //否则交互父节点和当前节点
		j = i        //继续向上调整
	}
}

//向下调整逻辑
func down(h Interface, i0, n int) bool {
	i := i0
	for {
		j1 := 2*i + 1
		if j1 >= n || j1 < 0 { // j1 < 0 after int overflow  溢出或者已经到堆底了，则跳出
			break
		}
		j := j1 // 左边子节点
		if j2 := j1 + 1; j2 < n && h.Less(j2, j1) {
			j = j2 // = 2*i + 2  // 右边节点存在并且比左节点的值更大(大顶堆)或更小(小顶堆) 则选择右节点
		}
		if !h.Less(j, i) { //不满足条件，跳出
			break
		}
		h.Swap(i, j) //交换，继续向下调整
		i = j
	}
	return i > i0 //判断是否有调整
}

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type Item struct {
	value    string // 优先级队列中的数据，可以是任意类型，这里使用string
	priority int    // 优先级队列中节点的优先级
	index    int    // index是该节点在堆中的位置
}

// 优先级队列需要实现heap的interface
type PriorityQueue []*Item

// 绑定Len方法
func (pq PriorityQueue) Len() int {
	return len(pq)
}

// 绑定Less方法，这里用的是小于号，生成的是小根堆
func (pq PriorityQueue) Less(i, j int) bool {
	return pq[i].priority < pq[j].priority
}

// 绑定swap方法
func (pq PriorityQueue) Swap(i, j int) {
	pq[i], pq[j] = pq[j], pq[i]
	pq[i].index, pq[j].index = i, j
}

// 绑定put方法，将index置为-1是为了标识该数据已经出了优先级队列了
func (pq *PriorityQueue) Pop() interface{} {
	old := *pq
	n := len(old)
	item := old[n-1]
	*pq = old[0 : n-1]
	item.index = -1
	return item
}

// 绑定push方法
func (pq *PriorityQueue) Push(x interface{}) {
	n := len(*pq)
	item := x.(*Item)
	item.index = n
	*pq = append(*pq, item)
}

// 更新修改了优先级和值的item在优先级队列中的位置
func (pq *PriorityQueue) update(item *Item, value string, priority int) {
	item.value = value
	item.priority = priority
	heap.Fix(pq, item.index)
}

func main() {
	// 创建节点并设计他们的优先级
	items := map[string]int{"二毛": 5, "张三": 3, "狗蛋": 9}
	i := 0
	pq := make(PriorityQueue, len(items)) // 创建优先级队列，并初始化
	for k, v := range items {             // 将节点放到优先级队列中
		pq[i] = &Item{
			value:    k,
			priority: v,
			index:    i}
		i++
	}
	heap.Init(&pq) // 初始化堆
	item := &Item{ // 创建一个item
		value:    "李四",
		priority: 1,
	}
	heap.Push(&pq, item)           // 入优先级队列
	pq.update(item, item.value, 6) // 更新item的优先级
	for len(pq) > 0 {
		item := heap.Pop(&pq).(*Item)
		fmt.Printf("%.2d:%s index:%.2d\n", item.priority, item.value, item.index)
	}
}