Quick Sort Algorithm in DSA C++ - 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 rearranging the array so that elements smaller than the pivot come before it, and elements greater come after. Then it sorts the smaller and greater parts separately.

beginner

What role does the 'pivot' play in Quick Sort?

The pivot divides the array into two parts: elements less than the pivot and elements greater than the pivot. This helps in sorting smaller parts independently.

intermediate

Explain the partition step in Quick Sort.

Partition rearranges the array so that all elements less than the pivot come before it, and all greater elements 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 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?

Because Quick Sort divides the problem into smaller parts and sorts them independently, it reduces the total number of comparisons and swaps, making it faster on average.

What does Quick Sort use to divide the array?

A A pivot element

B A temporary array

C A stack

D A queue

Quick Sort picks a pivot element to divide the array into smaller and greater parts.

What is the average time complexity of Quick Sort?

A O(n log n)

B O(n^2)

C O(log n)

D O(n)

Quick Sort has an average time complexity of O(n log n).

After partitioning, where is the pivot element placed?

A At the beginning of the array

B In its correct sorted position

C At the end of the array

D Randomly in the array

The pivot is placed in its correct sorted position after partitioning.

Which of these is NOT a step in Quick Sort?

A Choosing a pivot

B Partitioning the array

C Merging sorted arrays

D Recursively sorting subarrays

Merging is part of Merge Sort, not Quick Sort.

What happens if the pivot is always the smallest or largest element?

A Quick Sort stops

B Quick Sort runs in O(n log n)

C Quick Sort runs faster

D Quick Sort runs in O(n^2)

If the pivot is always smallest or largest, Quick Sort degrades to O(n^2) time.

Describe how Quick Sort sorts an array step-by-step.

Think about dividing the array around a pivot and sorting smaller parts.

Explain why Quick Sort is considered a divide and conquer algorithm.

Focus on how the problem is broken down and solved.