学习golang难免需要分析源码包中一些实现，下面就来说说container/heap包的源码
heap的实现使用到了小根堆，下面先对堆做个简单说明
1. 堆概念
堆是一种经过排序的完全二叉树，其中任一非终端节点的数据值均不大于（或不小于）其左孩子和右孩子节点的值。
最大堆和最小堆是二叉堆的两种形式。
最大堆：根结点的键值是所有堆结点键值中最大者。
最小堆：根结点的键值是所有堆结点键值中最小者。
2. heap
树的最小元素在根部，为index 0.
heap包对任意实现了heap接口的类型提供堆操作。
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。
// Any type that implements heap.Interface 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.
}
// A type, typically a collection, that satisfies sort.Interface can be
// sorted by the routines in this package. The methods require that the
// elements of the collection be enumerated by an integer index.
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)
}
根据上面interface的定义，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()， Less() ， Swap() 。
同事还需要实现堆接口定义的两个方法：Push(x interface{}) / Pop() interface{}， 所以我们要想使用heap定义一个堆， 只需要定义实现了这五个方法结构就可以了。
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 <= i < h.Len() and *i+ <= j <= *i+ 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。
以下是heap导出的方法：
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()。
实例：
1. 包含int的最小堆
// This example demonstrates an integer heap built using the heap interface.
package heap_test 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-]
*h = old[ : n-]
return x
} // This example inserts several ints into an IntHeap, checks the minimum,
// and removes them in order of priority.
func Example_intHeap() {
h := &IntHeap{, , }
heap.Init(h)
heap.Push(h, )
fmt.Printf("minimum: %d\n", (*h)[])
for h.Len() > {
fmt.Printf("%d ", heap.Pop(h))
}
// Output:
// minimum: 1
// 1 2 3 5
}
2. 用heap创建一个优先级队列
// 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-]
item.index = - // for safety
*pq = old[ : n-]
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 Example_priorityQueue() {
// Some items and their priorities.
items := map[string]int{
"banana": , "apple": , "pear": ,
} // Create a priority queue, put the items in it, and
// establish the priority queue (heap) invariants.
pq := make(PriorityQueue, len(items))
i :=
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: ,
}
heap.Push(&pq, item)
pq.update(item, item.value, ) // Take the items out; they arrive in decreasing priority order.
for pq.Len() > {
item := heap.Pop(&pq).(*Item)
fmt.Printf("%.2d:%s ", item.priority, item.value)
}
// Output:
// 05:orange 04:pear 03:banana 02:apple
}
说明：测试源码都是golang包里面提供的， 有兴趣可以直接去查阅下golang源码