python - 为什么 _siftup 和 _siftdown 在 Python 中正好相反？

Question

来自binary heap的定义在维基百科中，sift-up 也称为 up-heap 操作，sift-down 称为 down-heap。

所以在堆(完全二叉树)中，up表示从叶到根，down表示从根到叶。

但是在python中，似乎恰恰相反。我对 siftup 和 siftdown 的含义感到困惑，并且在我第一次使用时被误用。

这里是heapq中_siftdown和_siftup的python版本实现:

# 'heap' is a heap at all indices >= startpos, except possibly for pos.  pos
# is the index of a leaf with a possibly out-of-order value.  Restore the
# heap invariant.
def _siftdown(heap, startpos, pos):
    newitem = heap[pos]
    # Follow the path to the root, moving parents down until finding a place
    # newitem fits.
    while pos > startpos:
        parentpos = (pos - 1) >> 1
        parent = heap[parentpos]
        if newitem < parent:
            heap[pos] = parent
            pos = parentpos
            continue
        break
    heap[pos] = newitem

def _siftup(heap, pos):
    endpos = len(heap)
    startpos = pos
    newitem = heap[pos]
    # Bubble up the smaller child until hitting a leaf.
    childpos = 2*pos + 1    # leftmost child position
    while childpos < endpos:
        # Set childpos to index of smaller child.
        rightpos = childpos + 1
        if rightpos < endpos and not heap[childpos] < heap[rightpos]:
            childpos = rightpos
        # Move the smaller child up.
        heap[pos] = heap[childpos]
        pos = childpos
        childpos = 2*pos + 1
    # The leaf at pos is empty now.  Put newitem there, and bubble it up
    # to its final resting place (by sifting its parents down).
    heap[pos] = newitem
    _siftdown(heap, startpos, pos)

为什么在python中相反？我已经在 wiki 和其他几篇文章中确认过。有什么我遗漏或误解的吗？

感谢阅读，非常感谢它能帮助我。 :)

Answer 1

查看维基百科页面上的引用资料，我发现了这一点:

Note that this paper uses Floyd's original terminology "siftup" for what is now called sifting down.

似乎不同的作者对什么是“上”和“下”有不同的引用。

但是，正如@Dan D 在评论中所写，无论如何您都不应该使用这些函数。