Sets Interview Questions
4 min read ·
These questions are commonly asked in FAANG-level interviews and test deep understanding of Python sets, including performance, mutability, edge cases, and real-world use.
Each question includes a clear explanation and working solution.
Question 1: What Is a Set and Why Is It Used?
Answer
A set is an unordered collection of unique elements.
It is used for:
- Removing duplicates
- Fast membership testing
- Mathematical set operations
Question 2: Difference Between List, Tuple, and Set?
Answer
| Feature | List | Tuple | Set |
|---|---|---|---|
| Ordered | Yes | Yes | No |
| Mutable | Yes | No | Yes |
| Duplicates | Yes | Yes | No |
| Indexing | Yes | Yes | No |
Question 3: Why Are Sets Faster Than Lists for Lookup?
Answer
Sets use hash tables, giving average time complexity O(1) for lookup.
Question 4: How Do You Remove Duplicates from a List?
Answer
Question 5: What Is the Difference Between remove() and discard()?
Answer
| Method | Error if Missing |
|---|---|
remove() | Yes |
discard() | No |
Question 6: What Does pop() Remove in a Set?
Answer
pop() removes a random element.Question 7: Can a Set Contain a List?
Answer
No. Only hashable (immutable) elements are allowed.
Question 8: Can Sets Be Dictionary Keys?
Answer
No, because sets are mutable.
Use
frozenset instead.Question 9: What Is a Frozen Set?
Answer
An immutable version of a set.
Used as dictionary keys and set elements.
Question 10: Difference Between set() and {}?
Answer
set() creates a set, {} creates a dictionary.Question 11: How Do You Find Common Elements Between Two Sets?
Answer
Question 12: How Do You Check If Two Sets Are Disjoint?
Answer
Question 13: Difference Between union() and update()?
Answer
| Method | Modifies Original |
|---|---|
union() | No |
update() | Yes |
Question 14: Predict the Output (Tricky)
Answer
Both print
{1, 2, 3} due to reference behavior.Question 15: Can You Sort a Set?
Answer
No, but you can convert it.
Question 16: Time Complexity of Set Operations?
Answer
| Operation | Average Time |
|---|---|
| Add | O(1) |
| Remove | O(1) |
| Lookup | O(1) |
| Union | O(n) |
| Intersection | O(n) |
Question 17: How Do You Loop Through a Set?
Answer
Question 18: Difference Between difference() and symmetric_difference()?
Answer
Question 19: Can a Set Contain a Tuple?
Answer
Yes, if tuple elements are immutable.
Question 20: When Should You Avoid Sets?
Answer
Avoid sets when:
- Order matters
- Duplicates are required
- Index-based access is needed
Use lists or tuples instead.
Interview Takeaways
- Sets provide fast lookups
- Unique values only
- Immutable elements required
frozensetis key for advanced usage- Frequently tested in FAANG interviews
- Strong conceptual clarity is essential
Mastering sets shows strong problem-solving and Python fundamentals, highly valued in FAANG interviews.