heap包对任意实现了heap接口的类型提供堆操作。（小根）堆是具有“每个节点都是以其为根的子树中最小值”属性的树。树的最小元素在根部，为index 0.

heap是常用的实现优先队列的方法。要创建一个优先队列，实现一个具有使用（负的）优先级作为比较的依据的Less方法的Heap接口，如此一来可用Push添加项目而用Pop取出队列最高优先级的项目。

type Interface

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

可以看出，这个堆结构继承自sort.Interface,而sort.Interface，需要实现三个方法：Len() int / Less(i,j int) bool / Swap(i,j int) 再加上堆接口定义的两个方法：Push(x interface{}) / Pop() interface{}。故只要实现了这五个方法，变定义了一个堆。

任何实现了本接口的类型都可以用于构建最小堆。最小堆可以通过heap.Init建立，数据是递增顺序或者空的话也是最小堆。最小堆的约束条件是：

!h.Less(j,i) for 0 <= i < h.Len() and 2*i+1 <= j <= 2*i+2 and j < h.Len()

注意接口的Push和Pop方法是供heap包调用的，请使用heap.Push和heap.Pop来向一个堆添加或者删除元素。

func Fix(h Interface,i int) // 在修改第i个元素后，调用本函数修复堆，比删除第i个元素后插入新元素更有效率。复杂度O(log(n))，其中n等于h.Len()。
func Init(h Interface) //初始化一个堆。一个堆在使用任何堆操作之前应先初始化。Init函数对于堆的约束性是幂等的（多次执行无意义），并可能在任何时候堆的约束性被破坏时被调用。本函数复杂度为O(n)，其中n等于h.Len()。
func Pop(h Interface) interface{} //删除并返回堆h中的最小元素（不影响约束性）。复杂度O(log(n))，其中n等于h.Len()。该函数等价于Remove(h,0)。
func Push(h Interface,x interface{}) //向堆h中插入元素x，并保持堆的约束性。复杂度O(log(n))，其中n等于h.Len()。
func Remove(h Interface,i int) interface{} //删除堆中的第i个元素，并保持堆的约束性。复杂度O(log(n))，其中n等于h.Len()。

举例说明其用法：

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{2,1,5,100,3,6,4,5}
	heap.Init(h)
	heap.Push(h,3)
	heap.Fix(h,3)
	fmt.Printf("minimum: %d\n",(*h)[0])
	for h.Len() > 0 {
		fmt.Printf("%d ",heap.Pop(h))
	}

}

利用heap创建一个优先级队列

// 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]
	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 \n",item.priority,item.value)
	}
}

参考： https://golang.org/pkg/container/heap/