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从Wikipedia 中对二叉堆sift-up的定义来看，也称为up-heap操作，sift-down称为down-heap.

所以在堆（完全二叉树）中，up意思是从叶子到根，也down就是从根到叶子。

但在python中，它似乎正好相反。我对siftupand的含义感到困惑siftdown，并且在我第一次使用时被误用。

这是_siftdown和_siftupin的 python 版本实现heapq：

# '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？

感谢您的阅读，我非常感谢它帮助我。:)

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1 回答 1

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查看维基百科页面上的参考资料，我发现了这一点：

请注意，本文使用 Floyd 的原始术语“siftup”来表示现在称为 sifting down的内容。

似乎不同的作者对“向上”和“向下”有不同的参考。

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功能。

于 2019-03-27T11:06:42.497 回答