数据结构与算法回顾（四）：golang 的 container 包

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

// A heap must be initialized before any of the heap operations
// can be used. Init is idempotent with respect to the heap invariants
// and may be called whenever the heap invariants may have been invalidated.
// Its complexity is O(n) where n = h.Len().
//
func Init(h Interface) {
	// heapify
	n := h.Len()
	for i := n/2 - 1; i >= 0; i-- {
		down(h, i, n)
	}
}

// 给定类型，需要调整的元素在数组中的索引以及 heap 的长度
// 将该元素下沉到该元素对应的子树合适的位置，从而满足该子树为最小堆
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
			break
		}
		j := j1 // left child
		if j2 := j1 + 1; j2 <n && h.Less(j2, j1) {
			j = j2 // = 2*i + 2  // right child
		}
		if !h.Less(j, i) {
      // 以及满足最小堆的要求了，退出
			break
		}
		h.Swap(i, j)
		i = j
	}
	return i > i0
}

// Push pushes the element x onto the heap. The complexity is
// O(log(n)) where n = h.Len().
func Push(h Interface, x interface{}) {
	h.Push(x)
	up(h, h.Len()-1)
}

func up(h Interface, j int) {
	for {
		i := (j - 1) / 2 // parent
		if i == j || !h.Less(j, i) {
			break
		}
		h.Swap(i, j)
		j = i
	}
}

// Pop removes the minimum element (according to Less) from the heap
// and returns it. The complexity is O(log(n)) where n = h.Len().
// It is equivalent to Remove(h, 0).
func Pop(h Interface) interface{} {
	n := h.Len() - 1
	h.Swap(0, n)
	down(h, 0, n)
	return h.Pop()
}

// Remove removes the element at index i from the heap.
// The complexity is O(log(n)) where n = h.Len().
//
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()
}

// Fix re-establishes the heap ordering after the element at index i has changed its value.
// Changing the value of the element at index i and then calling Fix is equivalent to,
// but less expensive than, calling Remove(h, i) followed by a Push of the new value.
// The complexity is O(log(n)) where n = h.Len().
func Fix(h Interface, i int) {
	if !down(h, i, h.Len()) {
		up(h, i)
	}
}

type IntHeap []int

func main() {
    h := &IntHeap{2, 1, 5, 13,11, 4, 3, 7, 9, 8, 0}
    heap.Init(h)                                // 将数组切片进行堆化
    fmt.Println(*h)
    fmt.Println(heap.Pop(h))                    // 调用 pop 0 返回移除的顶部最小元素
    heap.Push(h, 6)                             // 添加一个元素进入堆中进行堆化
    for len(*h) > 0 {
      fmt.Printf("%d \n", heap.Pop(h))
    }
}

func (h IntHeap) Len() int { return len(h) }

func (h IntHeap) Less(i, j int) bool { return h[i] < h[j] }   //minheap

func (h IntHeap) Swap(i, j int) {
        h[i], h[j] = h[j], h[i]
}

func (h *IntHeap) Pop() interface{} {
    old := *h
    n := len(old)
    // 将顶小堆元素与最后一个元素交换位置，在进行堆排序的结果
    x := old[n-1]
    *h = old[0 : n-1]
    return x
}

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