Python: Sort a list of elements using Heap sort

Last update on April 02 2025 05:26:04 (UTC/GMT +8 hours)

17. Heap Sort

Write a Python program to sort a list of elements using Heap sort.
In computer science, heapsort (invented by J. W. J. Williams in 1964) is a comparison-based sorting algorithm. Heapsort can be thought of as an improved selection sort: like that algorithm, it divides its input into a sorted and an unsorted region, and it interactively shrinks the unsorted region by extracting the largest element and moving that to the sorted region. The improvement consists of the use of a heap data structure rather than a linear-time search to find the maximum. Although somewhat slower in practice on most machines than a well-implemented quicksort, it has the advantage of a more favorable worst-case O(n log n) runtime. Heapsort is an in-place algorithm, but it is not a stable sort. A run of the heapsort algorithm sorting an array of randomly permuted values. In the first stage of the algorithm the array elements are reordered to satisfy the heap property. Before the actual sorting takes place, the heap tree structure is shown briefly for illustration.

Sample Solution:

Python Code:

def heap_data(nums, index, heap_size):
    largest_num = index
    left_index = 2 * index + 1
    right_index = 2 * index + 2
    if left_index < heap_size and nums[left_index] > nums[largest_num]:
        largest_num = left_index

    if right_index < heap_size and nums[right_index] > nums[largest_num]:
        largest_num = right_index
    if largest_num != index:
        nums[largest_num], nums[index] = nums[index], nums[largest_num]
        heap_data(nums, largest_num, heap_size)
def heap_sort(nums):
    n = len(nums)
    for i in range(n // 2 - 1, -1, -1):
        heap_data(nums, i, n)
    for i in range(n - 1, 0, -1):
        nums[0], nums[i] = nums[i], nums[0]
        heap_data(nums, 0, i)
    return nums
user_input = input("Input numbers separated by a comma:\n").strip()
nums = [int(item) for item in user_input.split(',')]
heap_sort(nums)
print(nums)

Sample Output:

Input numbers separated by a comma:
 15, 79, 28, 35, 68
[15, 28, 35, 68, 79]

Flowchart:

For more Practice: Solve these Related Problems:

• Write a Python program to implement heap sort and display the heap structure before and after sorting.
• Write a Python script to sort a list using heap sort and count the number of comparisons during the heap construction phase.
• Write a Python program to use heap sort to sort a list of tuples based on a specified key.
• Write a Python function to implement heap sort and then validate the sorted order by comparing it with merge sort results.

Python Code Editor:

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