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Overview ¶
Example (IntHeap) ¶
This example inserts several ints into an IntHeap, checks the minimum, and removes them in order of priority.
// This example demonstrates an integer heap built using the heap interface.
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}
heap.Init(h)
heap.Push(h, 3)
fmt.Printf("minimum: %d\n", (*h)[0])
for h.Len() > 0 {
fmt.Printf("%d ", heap.Pop(h))
}
}
Output: minimum: 1 1 2 3 5
Example (PriorityQueue) ¶
This example creates a PriorityQueue with some items, adds and manipulates an item, and then removes the items in priority order.
// 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]
old[n-1] = nil // avoid memory leak
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 ", item.priority, item.value)
}
}
Output: 05:orange 04:pear 03:banana 02:apple
Index ¶
- type Heap
- func (hp *Heap[T]) AppendHeap(x []*T)
- func (hp *Heap[T]) Delete(ii int) (rv *T)
- func (hp *Heap[T]) Dump(fp io.Writer)
- func (hp *Heap[T]) Fix(ii int, newValue *T)
- func (hp *Heap[T]) GetValue(ii int) (value *T)
- func (hp *Heap[T]) Heapify(n, i int)
- func (hp *Heap[T]) Len() int
- func (hp *Heap[T]) Length() int
- func (hp *Heap[T]) Peek() (rv *T)
- func (hp *Heap[T]) Pop() (rv *T)
- func (hp *Heap[T]) Push(x *T)
- func (hp *Heap[T]) Search(cmpVal *T) (rv *T, pos int, err error)
- func (hp *Heap[T]) SetValue(ii int, newValue *T)
- func (hp *Heap[T]) Truncate()
Examples ¶
Constants ¶
This section is empty.
Variables ¶
This section is empty.
Functions ¶
This section is empty.
Types ¶
type Heap ¶
type Heap[T comparable.Comparable] struct { // contains filtered or unexported fields }
The heap data is stored in a slice of type *T
func NewHeap ¶
func NewHeap[T comparable.Comparable]() *Heap[T]
Create a new heap and return it. Complexity is O(1).
func (*Heap[T]) AppendHeap ¶
func (hp *Heap[T]) AppendHeap(x []*T)
AppendHeap appends a new set of data to the heap (and leaves the heap in a non-heap state). After 1..n AppendHeap operations a call to Heapify() is necessary to re-heap the heap.
Example: `h.Heapify(h.Len(),0)` will re-build the entire heap.
func (*Heap[T]) Delete ¶
Delete removes and returns the element at the specified index `ii` from the heap. Complexity is O(log n).
func (*Heap[T]) Fix ¶
Fix re-establishes the heap ordering after a change to the value of the element at locaiton `ii`. Changing the value of the element (indrement/decrement/update) at `ii` followed by a call to Fix() is the same as hp.Delete(ii) and hp.Push(NewValue). It is less expesive to call use the Fix operation. Complexity is O(log n).
func (*Heap[T]) GetValue ¶
GetValue will return the value at index `ii` in the heap. Complexity is O(1).
func (*Heap[T]) Heapify ¶
xyzzzy- Commnet- To heapify a subtree rooted with node i which is an index in arr[]. N is size of heap Heapify starts at the sub-tree at 'i' and re-construts the heap. This is useful after an AppendHeap operation. `h.Heapify(h.Len(),0)` will re-build the entire heap.
func (*Heap[T]) Pop ¶
func (hp *Heap[T]) Pop() (rv *T)
Pop removes and returns the minimum element (using comparable.Compare). Pop is the same as hp.Remove(0). Complexity is O(log n).
func (*Heap[T]) Push ¶
func (hp *Heap[T]) Push(x *T)
Push appends the element x onto the end of the heap and re-orders the heap to be a heap. Complexity is O(log n).
Source Files