Daily Coding Quiz: Sunday, 1 November 2026

All 10 coding questions with answers and explanations. 0 players took part.

1. Which sorting algorithm repeatedly swaps adjacent elements that are in the wrong order?

   DSA · easy

   1. Merge sort
   2. Quick sort
   3. Bubble sort
   4. Heap sort

   Answer: C. Bubble sort

   Explanation: Bubble sort compares neighbours and swaps them, so large values “bubble” to the end on each pass. It is O(n²).

2. Which of these is immutable?

   Python · easy

   1. list
   2. dict
   3. set
   4. tuple

   Answer: D. tuple

   Explanation: A tuple cannot be changed after it is created, which is also why tuples (of hashable items) can be dictionary keys.

3. Which clause filters groups after GROUP BY?

   SQL · easy

   1. WHERE
   2. HAVING
   3. ORDER BY
   4. LIMIT

   Answer: B. HAVING

   Explanation: WHERE filters rows before grouping; HAVING filters the groups, so it can use aggregates like COUNT(*) > 5.

4. What is the space complexity of a recursive DFS on a tree of height h (ignoring the output)?

   DSA · medium

   1. O(1)
   2. O(h)
   3. O(n log n)
   4. O(2^h)

   Answer: B. O(h)

   Explanation: The call stack holds one frame per level on the current root-to-node path, so at most h + 1 frames.

5. Which statements about gradient boosting (e.g. XGBoost, LightGBM) are true? (Select all that apply)

   Machine Learning · medium

   1. Trees are built one after another, each correcting the previous errors
   2. Trees are built independently in parallel like a random forest
   3. A learning rate shrinks each tree’s contribution
   4. It can overfit if you add too many trees

   Answer: A. Trees are built one after another, each correcting the previous errors; C. A learning rate shrinks each tree’s contribution; D. It can overfit if you add too many trees

   Explanation: Boosting is sequential: each tree fits the residual errors (gradients) of the current ensemble. Shrinkage and early stopping keep it from overfitting.

6. In a Transformer, why is positional information added to the token embeddings?

   AI & GenAI · medium

   1. To save memory
   2. Self-attention by itself ignores order, so position must be encoded explicitly
   3. To normalise the inputs
   4. To make tokens unique

   Answer: B. Self-attention by itself ignores order, so position must be encoded explicitly

   Explanation: Attention treats its input as a set. Sinusoidal, learned or rotary (RoPE) position encodings tell the model where each token is.

7. Predicted box A and ground-truth box B each have area 100 and overlap by 50. What is their IoU?

   Computer Vision · medium

   1. 0.25
   2. 0.33
   3. 0.5
   4. 0.67

   Answer: B. 0.33

   Explanation: IoU = intersection / union = 50 / (100 + 100 − 50) = 50 / 150 ≈ 0.33.

8. What is the minimum number of comparisons any comparison-based sort needs in the worst case?

   DSA · hard

   1. Θ(n)
   2. Θ(n log n)
   3. Θ(n²)
   4. Θ(log n)

   Answer: B. Θ(n log n)

   Explanation: There are n! possible orders, and a decision tree with n! leaves has height ≥ log₂(n!) = Θ(n log n). Counting sort beats this only by not comparing.

9. What is printed?

   Python · hard

   print(all([]), any([]), bool([[]]))

   1. True False True
   2. False False False
   3. True True True
   4. False False True

   Answer: A. True False True

   Explanation: all() of nothing is True (no element is false), any() of nothing is False. [[]] is a non-empty list, so it is truthy even though its item is empty.

10. What does the running total return for the third row?

    SQL · hard

    SELECT d, amt, SUM(amt) OVER (ORDER BY d) AS running
    FROM sales;
    -- rows (d, amt): ('2026-01-01', 10), ('2026-01-02', 20), ('2026-01-02', 5), ('2026-01-03', 7)

    1. 30
    2. 35
    3. 5
    4. 42

    Answer: B. 35

    Explanation: With ORDER BY and no frame clause the default frame is RANGE … CURRENT ROW, which includes all peers with the same d. Both 2026-01-02 rows show 10 + 20 + 5 = 35. Use ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW for a strict row-by-row total.

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