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

Recall & Review

beginner

What is the main idea behind the Quick Sort algorithm?

Quick Sort picks a 'pivot' element and divides the list into two parts: elements smaller than the pivot and elements larger than 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 smaller and larger parts. It helps organize the list so that all smaller elements come before it and all larger elements come after it.

intermediate

Explain the partition step in Quick Sort.

Partition rearranges the list so that elements less than the pivot are on the left, and elements greater than the pivot are on the right. 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. This means it sorts efficiently for most cases.

beginner

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

Quick Sort uses divide and conquer to break the problem into smaller parts, sorting them quickly and combining results. Bubble Sort compares and swaps elements repeatedly, which is slower.

What does Quick Sort use to divide the list?

A A pivot element

B A temporary array

C A stack

D A queue

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

What happens to the pivot after partitioning?

A It stays in the same place

B It moves to its correct sorted position

C It swaps with the first element

D It is removed from the list

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

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

A O(n)

B O(n log n)

C O(n^2)

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 technique does Quick Sort use?

A Divide and conquer

B Dynamic programming

C Greedy algorithm

D Backtracking

Quick Sort uses divide and conquer by splitting the list and sorting parts separately.

Which of these is NOT a step in Quick Sort?

A Recursively sorting sublists

B Partitioning the list

C Choosing a pivot

D Merging sorted lists

Quick Sort does not merge sorted lists; it sorts in place after partitioning.

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 is efficient on average but can be slow in the worst case.

Consider how the pivot affects the splits.