A Deep Dive into Heap and Heap Sort in Python: From Beginner to Expert

heap_sort.py

def heap_sort(arr):
    # Build a max heap from the input list
    heapify(arr)
    # Extract the root element (the maximum value) and place it at the end of the sorted list
    sorted_arr = []
    while arr:
        sorted_arr.append(heappop(arr))
    # Return the sorted list
    return sorted_arr


def heapify(arr):
    # Start from the last non-leaf node and heapify all nodes from bottom to top
    n = len(arr)
    for i in range(n // 2 - 1, -1, -1):
        heapify_node(arr, i, n)


def heapify_node(arr, i, n):
    # Heapify the node at index i and its children
    left = 2 * i + 1
    right = 2 * i + 2
    largest = i
    if left < n and arr[left] > arr[largest]:
        largest = left
    if right < n and arr[right] > arr[largest]:
        largest = right
    if largest != i:
        arr[i], arr[largest] = arr[largest], arr[i]
        heapify_node(arr, largest, n)


def heappop(arr):
    # Extract the root element (the maximum value) from the heap
    root = arr[0]
    arr[0] = arr[-1]
    del arr[-1]
    heapify(arr)
    return root


print(heap_sort([5, 2, 7, 2077, 3, 99, 4, 54, 20]))
# [2077, 99, 54, 20, 7, 5, 4, 3, 2]