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/*
binary heap (min-heap) algorithm used as a core for the priority queue
*/
package priorityqueue
type BinHeap []PQItem
func NewBinHeap() *BinHeap {
return &BinHeap{}
}
func (bh *BinHeap) Init(items []PQItem) {
arraySize := len(items) - 1
for i := arraySize/2 - 1; i >= 0; i-- {
bh.shiftDown(items, i, arraySize)
}
for i := arraySize - 1; i >= 1; i-- {
items[0], items[i] = items[i], items[0]
bh.shiftDown(items, 0, i-1)
}
}
func (bh *BinHeap) shiftDown(numbers []PQItem, k, n int) {
// k << 1 is equal to k*2
for k<<1 <= n {
j := k << 1
if j < n && numbers[j].Priority() < numbers[j+1].Priority() {
j++
}
if !(numbers[k].Priority() < numbers[j].Priority()) {
break
}
numbers[k], numbers[j] = numbers[j], numbers[k]
k = j
}
}
func (bh *BinHeap) fix() {}
func (bh *BinHeap) Push(_ PQItem) {}
func (bh *BinHeap) Pop() PQItem {
bh.fix()
// get min
return nil
}
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