Heap sort

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

        if l < n and arr[largest] < arr[l]:
            largest = l

        if r < n and arr[largest] < arr[r]:
            largest = r

        if largest != i:
            arr[i], arr[largest] = arr[largest], arr[i]
            heapify(arr, n, largest)

    n = len(arr)

    for i in range(n//2 - 1, -1, -1):
        heapify(arr, n, i)

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