heap
最后更新于：2022-04-02 02:42:35
[TOC]
## heap 堆
> 堆使用的数据结构是最小二叉树，即根节点比左边子树和右边子树的所有值都小。
```
type Interface
func Init(h Interface)
func Push(h Interface, x interface{})
func Pop(h Interface) interface{}
func Remove(h Interface, i int) interface{}
func Fix(h Interface, i int)
```
## 实例
### 初始化 help
```
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{}) {
//限制为整数
if n, ok := x.(int); ok {
*h = append(*h, n)
}
}
func (h *IntHeap) Pop() interface{} {
old := *h
n := len(old)
x := old[n-1]
*h = old[0 : n-1]
return x
}
func main() {
h := &IntHeap{2, 1, 5}
heap.Init(h)
heap.Push(h, 3)
fmt.Println(h) // &[1 2 5 3]
// pop 推出最小的元素
heap.Pop(h)
fmt.Println(h) // &[2 3 5]
heap.Pop(h)
fmt.Println(h) // &[3 5]
}
```
### 含优先级的堆
```
type Item struct {
value string
priority int // 项的优先级队列
index int
}
type PriorityQueue []*Item
func (pq PriorityQueue) Len() int { return len(pq) }
func (pq PriorityQueue) Less(i, j int) bool {
// 用过优先级比较
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)
}
func main() {
items := map[string]int{
"banana": 3, "apple": 2, "pear": 4,
}
pq := make(PriorityQueue, len(items))
i := 0
for value, priority := range items {
pq[i] = &Item{
value: value,
priority: priority,
index: i,
}
i++
}
// 初始化堆
heap.Init(&pq)
// 插入新值,并跟新 pq
item := &Item{
value: "orange",
priority: 1,
}
heap.Push(&pq, item)
pq.update(item, item.value, 5)
for pq.Len() > 0 {
item := heap.Pop(&pq).(*Item)
fmt.Printf("%.2d:%s ", item.priority, item.value)
}
// Output:
// 05:orange 04:pear 03:banana 02:apple
}
```
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