python - Python heapsort实现说明

这是heapsort的python3实现，其中n是堆的大小。

def heapify(arr, n, i):
    largest = i
    l = 2 * i + 1     # left = 2*i + 1
    r = 2 * i + 2     # right = 2*i + 2

# See if left child of root exists and is
# greater than root
if l < n and arr[i] < arr[l]:
    largest = l

# See if right child of root exists and is
# greater than root
if r < n and arr[largest] < arr[r]:
    largest = r

# Change root, if needed
if largest != i:
    arr[i],arr[largest] = arr[largest],arr[i] # swap

    # Heapify the root.
    heapify(arr, n, largest)

# The main function to sort an array of given size
def heapSort(arr):
   n = len(arr)

   # Build a maxheap.
   for i in range(n, -1, -1):
       heapify(arr, n, i)

# One by one extract elements
for i in range(n-1, 0, -1):
    arr[i], arr[0] = arr[0], arr[i] # swap
    heapify(arr, i, 0)

我知道医疗功能和它在做什么不过，我在max heap中看到了一个问题：

for i in range(n, -1, -1):

根据我的研究，我认为我需要在非叶节点上只构建最大堆，它应该是0…N/2.那么这里的范围正确吗？
我也很难理解最后一部分：

for i in range(n-1, 0, -1):
arr[i], arr[0] = arr[0], arr[i] # swap
heapify(arr, i, 0)

从n-1开始这个范围是如何工作的步骤为-1的0？

最佳答案

c语言中HeapSort的geeksforgeks代码++

// Build heap (rearrange array)
for (int i = n / 2 - 1; i >= 0; i--)
    heapify(arr, n, i);

参考：-
GeeksforGeeks
CLRS手册中Heapsort的伪代码

BUILD-MAX-HEAP(A)
    heap-size[A] ← length[A]
    for i ← length[A]/2 downto 1
    do MAX-HEAPIFY(A, i)

所以是的，你是对的仅堆非叶节点就足够了。
至于你的第二个问题：-
伪码

1.MaxHeapify(Array)
2.So the Array[0] has the maximum element
3.Now exchange Array[0] and Array[n-1] and decrement the size of heap by 1.
4.So we now have a heap of size n-1 and we again repeat the steps 1,2 and 3 till the index is 0.