Heap Sort Algorithm in DSA Go - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the main idea behind the Heap Sort algorithm?

Heap Sort uses a special tree structure called a heap to sort elements. It builds a max-heap to repeatedly extract the largest element and place it at the end of the list, sorting the array in-place.

beginner

What is a max-heap?

A max-heap is a binary tree where each parent node is greater than or equal to its children. This property helps quickly find the largest element at the root.

intermediate

Why does Heap Sort have O(n log n) time complexity?

Building the heap takes O(n) time, and each of the n elements is extracted with a heapify operation that takes O(log n), resulting in O(n log n) overall.

intermediate

What is the role of the heapify function in Heap Sort?

Heapify ensures the heap property is maintained by fixing the subtree rooted at a given index, making sure the parent node is larger than its children.

intermediate

Is Heap Sort a stable sorting algorithm? Why or why not?

Heap Sort is not stable because it can change the relative order of equal elements during the heapify and extraction steps.

What data structure does Heap Sort primarily use?

A Queue

B Linked List

C Heap

D Stack

Heap Sort uses a heap data structure to organize elements for sorting.

In a max-heap, where is the largest element located?

A At the leaves

B At the root

C In the middle

D At the last node

The largest element in a max-heap is always at the root node.

What is the time complexity of Heap Sort in the average case?

A O(n log n)

B O(n^2)

C O(log n)

D O(n)

Heap Sort runs in O(n log n) time on average due to heap construction and repeated heapify operations.

Which step is NOT part of Heap Sort?

A Building a max-heap

B Extracting the max element

C Heapifying the remaining elements

D Merging sorted subarrays

Merging sorted subarrays is part of Merge Sort, not Heap Sort.

Is Heap Sort an in-place sorting algorithm?

A Yes

B No

C Only for small arrays

D Depends on the implementation

Heap Sort sorts the array in-place without needing extra space proportional to input size.

Explain how Heap Sort uses a max-heap to sort an array step-by-step.

Think about how the largest element moves to the end each time.

Describe the heapify process and why it is important in Heap Sort.

Heapify keeps the tree organized after changes.