dissertation-2-code/utils/heap.go

package utils

import "errors"

var ErrorEmptyHeap = errors.New("attempted to extract from empty heap")

// A MinHeap for Uint64
type Uint32Heap []uint32

func (h *Uint32Heap) swap(x, y int) {
	(*h)[x] = (*h)[x] ^ (*h)[y]
	(*h)[y] = (*h)[y] ^ (*h)[x]
	(*h)[x] = (*h)[x] ^ (*h)[y]
}

func (h *Uint32Heap) Insert(new uint32) uint32 {
	*h = append(*h, new)

	child := len(*h) - 1
	for child != 0 {
		parent := (child - 1) / 2
		if (*h)[parent] > (*h)[child] {
			h.swap(parent, child)
		} else {
			break
		}
		child = parent
	}

	return (*h)[0]
}

func (h *Uint32Heap) Extract() (uint32, error) {
	if len(*h) == 0 {
		return 0, ErrorEmptyHeap
	}
	min := (*h)[0]

	(*h)[0] = (*h)[len(*h)-1]
	*h = (*h)[:len(*h)-1]

	parent := 0
	for {
		left, right := parent*2+1, parent*2+2

		if (left < len(*h) && (*h)[parent] > (*h)[left]) || (right < len(*h) && (*h)[parent] > (*h)[right]) {
			if right < len(*h) && (*h)[left] > (*h)[right] {
				h.swap(parent, right)
				parent = right
			} else {
				h.swap(parent, left)
				parent = left
			}
		} else {
			return min, nil
		}
	}
}

func (h *Uint32Heap) Peek() (uint32, error) {
	if len(*h) == 0 {
		return 0, ErrorEmptyHeap
	}
	return (*h)[0], nil
}