built-in max heap API in Python

Question

Default heapq is min queue implementation and wondering if there is an option for max queue? Thanks.

I tried the solution using _heapify_max for max heap, but how to han

Answer 1

There is a _heappop_max function in the latest cpython source that you may find useful:

def _heappop_max(heap):
    """Maxheap version of a heappop."""
    lastelt = heap.pop()    # raises appropriate IndexError if heap is empty
    if heap:
        returnitem = heap[0]
        heap[0] = lastelt
        heapq._siftup_max(heap, 0)
        return returnitem
    return lastelt

If you change the heappush logic using heapq._siftdown_max you should get the desired output:

def _heappush_max(heap, item):
    heap.append(item)
    heapq._siftdown_max(heap, 0, len(heap)-1)


def _heappop_max(heap):
    """Maxheap version of a heappop."""
    lastelt = heap.pop()  # raises appropriate IndexError if heap is empty
    if heap:
        returnitem = heap[0]
        heap[0] = lastelt
        heapq._siftup_max(heap, 0)
        return returnitem
    return lastelt


def heapsort2(iterable):
    h = []
    heapq._heapify_max(h)
    for value in iterable:
        _heappush_max(h, value)
    return [_heappop_max(h) for i in range(len(h))]

Output:

In [14]: heapsort2([1,3,6,2,7,9,0,4,5,8])
Out[14]: [9, 8, 7, 6, 5, 4, 3, 2, 1, 0]

In [15]: heapsort2([7, 8, 9, 6, 4, 2, 3, 5, 1, 0])
Out[15]: [9, 8, 7, 6, 5, 4, 3, 2, 1, 0]

In [16]: heapsort2([19,13,15,17,11,10,14,20,18])
Out[16]: [20, 19, 18, 17, 15, 14, 13, 11, 10]

In [17]: heapsort2(["foo","bar","foobar","baz"])
Out[17]: ['foobar', 'foo', 'baz', 'bar']