// 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-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 Example_intHeap() {
 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
}

// 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-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)
}
// 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": 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
}