heap_sort.py

# This program is an implementation of the HeapSort algorithm made in python3.
#
# This program first asks for the amount of numbers to order. Then the user
# should enter number separated with an enter and after every number has been
# entered the program will return the numbers in the correct order.

arr = [] # Empty list initialization
n = int(input("Enter the number of elements: "))
print("Enter your numbers:")

for i in range(n):
    arr.append(int(input()))

def heapify(arr, n, i):
    largest = i  # Initialize largest as root
    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 heap_sort(arr):
    n = len(arr)

    # Build a maxheap.
    # Since last parent will be at ((n//2)-1) we can start at that location.
    for i in range(n // 2 - 1, -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)

heap_sort(arr)

print ("Sorted array:")
for i in range(len(arr)):
    print ("%d" %arr[i])