Quick Sort Algorithm in DSA Javascript - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the main idea behind the Quick Sort algorithm?

Quick Sort works by picking a 'pivot' element and dividing the list into two parts: elements less than the pivot and elements greater than or equal to the pivot. It then sorts these parts separately and combines them.

beginner

What role does the pivot play in Quick Sort?

The pivot is the element used to split the list into two parts. Elements smaller than the pivot go to one side, and elements larger or equal go to the other side. This helps in sorting the list efficiently.

intermediate

Explain the partition step in Quick Sort.

Partition rearranges the list so that all elements less than the pivot come before it, and all elements greater or equal come after. The pivot ends up in its correct sorted position.

intermediate

What is the average time complexity of Quick Sort?

The average time complexity of Quick Sort is O(n log n), where n is the number of elements to sort.

beginner

Why can Quick Sort be faster than other sorting algorithms like Bubble Sort?

Quick Sort divides the problem into smaller parts and sorts them independently, which reduces the total work. Bubble Sort compares and swaps elements repeatedly, which is slower for large lists.

What does Quick Sort use to divide the list?

A A stack

B A temporary array

C A pivot element

D A queue

Quick Sort uses a pivot element to split the list into smaller parts.

What happens to the pivot after partitioning?

A It swaps with the last element

B It stays at the start of the list

C It is removed from the list

D It moves to its correct sorted position

After partitioning, the pivot is placed where all smaller elements are left and larger or equal are right, so it is in the correct position.

What is the worst-case time complexity of Quick Sort?

A O(n log n)

B O(n^2)

C O(n)

D O(log n)

In the worst case, Quick Sort can take O(n^2) time, for example when the smallest or largest element is always chosen as pivot.

Which of these is NOT a step in Quick Sort?

A Merging sorted lists

B Choosing a pivot

C Partitioning the list

D Recursively sorting sublists

Quick Sort does not merge sorted lists; it sorts in place by partitioning and recursion.

Why is Quick Sort considered efficient on average?

A Because it divides the list and sorts parts independently

B Because it sorts by swapping adjacent elements only

C Because it uses extra memory

D Because it always picks the middle element as pivot

Quick Sort is efficient because it breaks the problem into smaller parts and sorts them separately.

Describe how Quick Sort sorts a list step-by-step.

Think about how the list is split and sorted in parts.

Explain why Quick Sort can be faster than simple sorting methods like Bubble Sort.

Focus on how Quick Sort handles the list differently.