4.2.7.1 Dictionaries and key-value pairs Quiz: AQA Computer Science, Unit 2

The 20 questions

1. What data structure consists of a collection of key-value pairs?

   • Binary tree
   • Queue
   • Stack
   • Dictionary

2. In a dictionary data structure, which component of each entry must be unique?

   • Pointer
   • Index
   • Value
   • Key

3. Which Python expression creates an empty dictionary?

   • []
   • ()
   • <>
   • {}

4. In an information retrieval dictionary built from a text document, what does each key represent?

   • A word
   • A line number
   • A word count
   • A character index

5. Which Python expression retrieves the value associated with key k in dictionary d?

   • d.k
   • d->k
   • d[k]
   • d(k)

6. In the dictionary {'grass': 1, 'green': 2, 'grows': 1}, what value is mapped to 'green'?

   • 0
   • 1
   • 2
   • 3

7. Which technique allows dictionaries to perform direct value lookups using keys?

   • Traversal
   • Sorting
   • Linear searching
   • Hashing

8. A dictionary d holds {'apple': 3, 'pear': 5}. After d['apple'] = d['apple'] + 1, what is d['apple']?

   • 5
   • 8
   • 3
   • 4

9. A word-count dictionary is built from the text 'The cat sat on the mat', ignoring letter case. What is the count stored for 'the'?

   • 2
   • 3
   • 6
   • 1

10. Given dictionary d = {'a': 1, 'b': 2}, what is len(d) after executing d['c'] = 3?

    • 4
    • 1
    • 3
    • 2

11. Dictionary scores = {'Ali': 55, 'Bea': 72, 'Cal': 61}. What does max(scores, key=scores.get) return?

    • 'Cal'
    • 72
    • 'Ali'
    • 'Bea'

12. Which statement removes the key 'pear' from dictionary d in Python?

    • d.delete(pear)
    • d.remove('pear')
    • d['pear'].clear()
    • del d['pear']

13. Using a list of key-value pairs instead of a dictionary, what is the worst-case number of key comparisons needed to find one key among 1000 entries?

    • 500
    • 1000
    • 1
    • 10

14. If word counts ignore case, what value maps to key 'the' for 'The cat and the hat'?

    • 2
    • 3
    • 1
    • 0

15. Why are student IDs preferred over student names as keys in a dictionary database?

    • IDs use memory
    • IDs are unique
    • Names are shorter
    • Names are unique

16. Given d = {'x': [1, 2], 'y': [3]}, what is d['x'] after executing d['x'].append(4)?

    • [1, 2, 3, 4]
    • [1, 2]
    • [1, 2, 4]
    • [4]

17. Dictionary lookup in Python is typically which order of complexity on average?

    • Exponential time, O(2^n)
    • Linear time, O(n)
    • Logarithmic time, O(log n)
    • Constant time, O(1)

18. What main advantage does a dictionary offer over a list when representing a sparse vector?

    • Faster sorting
    • Prevents errors
    • Saves memory
    • Guarantees order

19. For dictionary d = {'a': 1, 'b': 2, 'a': 5}, what value is stored at key 'a'?

    • 1
    • 2
    • 6
    • 5

20. When representing a vector as a dictionary, what do the keys typically represent?

    • Vector indices
    • Coordinate angles
    • Vector magnitudes
    • Scalar multipliers

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