Sorting Stability and When to Use Which Sort in DSA Javascript - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does it mean for a sorting algorithm to be stable?

A stable sorting algorithm keeps the original order of equal elements the same after sorting.

beginner

Name a common stable sorting algorithm.

Merge Sort is a common stable sorting algorithm.

intermediate

Why might you choose an unstable sort like Quick Sort over a stable sort?

Quick Sort is often faster and uses less memory, so it is chosen when speed and space are more important than keeping equal elements in order.

beginner

Which sorting algorithm is best for nearly sorted data and why?

Insertion Sort is best for nearly sorted data because it runs very fast when the list is almost sorted.

intermediate

What is a key factor in deciding which sorting algorithm to use?

Key factors include data size, whether stability is needed, memory limits, and if the data is nearly sorted or random.

Which sorting algorithm is stable by default?

A Quick Sort

B Merge Sort

C Heap Sort

D Selection Sort

Merge Sort keeps equal elements in their original order, making it stable.

When is Insertion Sort a good choice?

A For very large random data

B When memory is very limited

C For nearly sorted data

D When stability is not important

Insertion Sort is efficient for nearly sorted data because it requires fewer moves.

Why might Quick Sort be preferred over Merge Sort?

A It uses less memory and is often faster

B It is stable

C It works better on nearly sorted data

D It is easier to implement

Quick Sort usually uses less memory and can be faster, but it is unstable.

What does an unstable sort do with equal elements?

A Keeps their original order

B Sorts only unique elements

C Removes duplicates

D May change their original order

Unstable sorts can reorder equal elements differently from their original order.

Which factor is NOT important when choosing a sorting algorithm?

A Color of the data

B Need for stability

C Data size

D Memory availability

The color of data is irrelevant; size, stability, and memory are important.

Explain what sorting stability means and give an example of when you would need a stable sort.

Think about keeping order of equal items.

Describe how you would choose a sorting algorithm based on data size, stability needs, and data order.

Match algorithm strengths to data conditions.