Go语言标准库堆(heap)封装及堆排序实现

Go语言的OOP,接口,接口的组合,基础库的函数及接口如何抽象设计,

这些东西在Go的Heap源码及演示例子处理中,都有很好的展示.

在"container/heap"中,它的接口是如下定义的:

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

我不太明白为啥是这样的设计,只好通过下面的方法来尝试了解.

1. 通过测试例子,了解使用方式.

2. 试图还原原始场景,即利用源码整合实现了一个原始的堆排序

然后通过这两者的对比,来慢慢体会.

container/heap的测试例子:

package main

import (
	"container/heap"
	"fmt"
	"sort"
)

// 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{100,16,4,8,70,2,36,22,5,12}

	fmt.Println("\nHeap:")
	heap.Init(h)

	fmt.Printf("最小值: %d\n", (*h)[0])

	//for(Pop)依次输出最小值,则相当于执行了HeapSort
	fmt.Println("\nHeap sort:")
	for h.Len() > 0 {
		fmt.Printf("%d ", heap.Pop(h))
	}

	//增加一个新值,然后输出看看
	fmt.Println("\nPush(h, 3),然后输出堆看看:")
	heap.Push(h, 3)
	for h.Len() > 0 {
		fmt.Printf("%d ", heap.Pop(h))
	}

	fmt.Println("\n使用sort.Sort排序:")
    h2 := IntHeap{100,16,4,8,70,2,36,22,5,12}
    sort.Sort(h2)
    for _,v := range h2 {
		fmt.Printf("%d ",v)
	}
}

/*
输出结果:
-----------------------------------
Heap:
最小值: 2

Heap sort:
2 4 5 8 12 16 22 36 70 100
Push(h, 3),然后输出堆看看:
3
使用sort.Sort排序:
2 4 5 8 12 16 22 36 70 100
*/

自定义的类,实现相关接口后,交由heap.Init()去构建堆.

从堆中Pop()后,数据就被从heap中移除了.

自定义类也可以直接用Sort来排序,因为实现了相关接口.

再看下我手工整合实现的堆排序代码:

package main

//Heap
//author:Xiong Chuan Liang
//date:2015-2-4

import (
	"fmt"
)

var(
  heap = []int{100,16,4,8,70,2,36,22,5,12}
)

func main(){
	fmt.Println("\n数组:")
	Print(heap)

    MakeHeap()
    fmt.Println("\n构建树后:")
	Print(heap)

	fmt.Println("\n增加 90,30,1 :")
	Push(90)
	Push(30)
	Push(1)
	Print(heap)	

	n := Pop()
	fmt.Println("\nPop出最小值(",n,")后:")
	Print(heap)	

	fmt.Println("\nRemove()掉idx为3即值",heap[3-1],"后:")
	Remove(3)
	Print(heap)	

	fmt.Println("\nHeapSort()后:")
	HeapSort()
	Print(heap)	

}

func Print(arr []int){
	for _,v := range arr {
		fmt.Printf("%d ",v)
	}
}

//构建堆
func MakeHeap(){
	n := len(heap)
	for i := n/2-1 ;i >= 0;i--{
		down(i, n)
	}
}

//由父节点至子节点依次建堆
//parent      : i
//left child  : 2*i+1
//right child : 2*i+2
func down(i,n int) {
	//构建最小堆,父小于两子节点值
	for {	

		j1 := 2*i + 1
		if j1 >= n || j1 < 0 { // j1 < 0 after int overflow
			break
		}

		//找出两个节点中最小的(less: a<b)
		j := j1 // left child
		if j2 := j1 + 1; j2 < n && !Less(j1, j2) {
			j = j2 // = 2*i + 2  // right child
		}

		//然后与父节点i比较,如果父节点小于这个子节点最小值,则break,否则swap
		if !Less(j, i) {
			break
		}
		Swap(i, j)
		i = j
	}
}

//由子节点至父节点依次重建堆
func up(j int)  {

	for {
		i := (j - 1) / 2 // parent      

		if i == j || !Less(j, i) {
			//less(子,父) !Less(9,5) == true
			//父节点小于子节点,符合最小堆条件,break
			break
		}
		//子节点比父节点小,互换
		Swap(i, j)
		j = i
	}
}

func Push(x interface{}){
	heap = append(heap, x.(int))
	up(len(heap)-1)
	return
}

func Pop() interface{} {
	n := len(heap) - 1
	Swap(0, n)
	down(0, n)

	old :=heap
	n = len(old)
	x := old[n-1]
	heap = old[0 : n-1]
	return x
}

func Remove(i int) interface{} {
	n := len(heap) - 1
	if n != i {
		Swap(i, n)
		down(i, n)
		up(i)
	}
	return Pop()
}

func Less(a,b int)bool{
	return heap[a] < heap[b]

func Swap(a,b int){
	heap[a],heap[b] = heap[b],heap[a]
}

func HeapSort(){
	//升序 Less(heap[a] > heap[b])	//最大堆
	//降序 Less(heap[a] < heap[b])	//最小堆
	for i := len(heap)-1 ;i > 0;i--{
		//移除顶部元素到数组末尾,然后剩下的重建堆,依次循环
		Swap(0, i)
		down(0, i)
	}
}

/*
输出结果:
-----------------------------------
数组:
100 16 4 8 70 2 36 22 5 12
构建树后:
2 5 4 8 12 100 36 22 16 70
增加 90,30,1 :
1 5 2 8 12 4 36 22 16 70 90 100 30
Pop出最小值( 1 )后:
2 5 4 8 12 30 36 22 16 70 90 100
Remove()掉idx为3即值 4 后:
4 5 8 16 12 30 36 22 100 70 90
HeapSort()后:
100 90 70 36 30 22 16 12 8 5 4

*/

两相对比之后发现,container/heap 竞然,真的,仅且只是封装了一个堆而已.

把那些不确定的,各种需要定制的东西,都交给了用户去实现.

它仅仅只负责最核心的堆这部份的东西.

这样基础库清爽了,使用堆时也不会再感到缚手缚脚了.

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