Arrays vs Other Data Structures When to Choose Arrays in DSA Python - Interactive Comparison Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create an array of size 5 initialized with zeros.

DSA Python

arr = [[1]] * 5
print(arr)

Drag options to blanks, or click blank then click option'

ANone

B0

C1

D''

Attempts:

3 left

💡 Hint

Common Mistakes

Using None instead of 0 will create an array of None values.

Using 1 will create an array of ones, not zeros.

The array is initialized with zeros by using 0 inside the list multiplied by 5.

2fill in blank

medium

Complete the code to access the third element of the array.

DSA Python

arr = [10, 20, 30, 40, 50]
print(arr[[1]])

Drag options to blanks, or click blank then click option'

A2

B1

C3

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using index 3 will access the fourth element, not the third.

Using index 1 will access the second element.

Arrays start at index 0, so the third element is at index 2.

3fill in blank

hard

Fix the error in the code to append an element to the array.

DSA Python

arr = [1, 2, 3]
arr.[1](4)
print(arr)

Drag options to blanks, or click blank then click option'

Aextend

Badd

Cinsert

Dappend

Attempts:

3 left

💡 Hint

Common Mistakes

Using add() causes an error because lists do not have add method.

Using insert() requires two arguments, so it will cause an error here.

The correct method to add an element at the end of a list (array) is append.

4fill in blank

hard

Fill both blanks to create a list of squares for numbers 1 to 5, but only include squares greater than 10.

DSA Python

squares = [x[1]2 for x in range(1, 6) if x[2]3]
print(squares)

Drag options to blanks, or click blank then click option'

A**

B%

C>

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using % instead of ** will calculate remainder, not square.

Using < instead of > will filter wrong numbers.

Use ** to square the number and > to filter numbers greater than 3.

5fill in blank

hard

Fill all three blanks to create a dictionary with keys as uppercase letters and values as their ASCII codes, but only for letters with ASCII code greater than 65.

DSA Python

result = { [1]: [2] for letter in ['a', 'B', 'C', 'd', 'E'] if ord(letter) [3] 65 }
print(result)

Drag options to blanks, or click blank then click option'

Aletter.upper()

Bord(letter)

C>

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using letter instead of letter.upper() will keep keys in original case.

Using < instead of > will filter wrong letters.

Use letter.upper() as keys, ord(letter) as values, and filter letters with ASCII code greater than 65.

Practice

1. Which of the following is the best reason to choose an array over a linked list?

easy

A. You want to store elements of different types

B. You want to easily insert elements in the middle

C. You want to save memory by avoiding unused space

D. You need fast access to elements by index

Solution

1. Step 1: Understand array access

   Arrays store elements in continuous memory, so accessing by index is very fast (constant time).

2. Step 2: Compare with linked list

   Linked lists require traversal from the start to access an element by index, which is slower.

3. Final Answer:

   You need fast access to elements by index -> Option D

4. Quick Check:

   Fast index access = Array [OK]

Hint: Arrays give quick index access, linked lists don't [OK]

Common Mistakes:

• Thinking arrays are better for middle insertions
• Confusing memory usage benefits
• Assuming arrays can store mixed types easily

2. Which of the following is the correct way to declare an array of 5 integers in Python using the array module?

easy

A. arr = array(5, 'i')

B. arr = array('i', [1, 2, 3, 4, 5])

C. arr = array([1, 2, 3, 4, 5], 'i')

D. arr = array('int', 5)

Solution

1. Step 1: Recall array module syntax

   The array constructor takes a type code string first, then an iterable of elements.

2. Step 2: Match correct syntax

   arr = array('i', [1, 2, 3, 4, 5]) uses array('i', [1, 2, 3, 4, 5]), which is correct for an integer array.

3. Final Answer:

   arr = array('i', [1, 2, 3, 4, 5]) -> Option B

4. Quick Check:

   array(typecode, iterable) = arr = array('i', [1, 2, 3, 4, 5]) [OK]

Hint: array(typecode, iterable) is the correct constructor [OK]

Common Mistakes:

• Swapping arguments order
• Using type names instead of type codes
• Passing size instead of iterable

3. What will be the output of the following code?

import array
arr = array.array('i', [10, 20, 30, 40])
print(arr[2])
arr[2] = 50
print(arr)

medium

A. [10, 20, 30, 40]\n[10, 20, 50, 40]

B. 30\n[10, 20, 50, 40]

C. 30\narray('i', [10, 20, 50, 40])

D. Error at arr[2] = 50

Solution

1. Step 1: Print element at index 2

   arr[2] is 30, so first print outputs 30.

2. Step 2: Update element and print array

   arr[2] = 50 updates the third element. Printing arr shows array('i', [10, 20, 50, 40]).

3. Final Answer:

   30\narray('i', [10, 20, 50, 40]) -> Option C

4. Quick Check:

   Index access and update work as expected [OK]

Hint: Array prints with typecode, index access returns element [OK]

Common Mistakes:

• Expecting list-like print output
• Thinking assignment causes error
• Confusing index positions

4. The following code tries to insert an element at the start of an array. What is the error and how to fix it?

import array
arr = array.array('i', [1, 2, 3])
arr.insert(0, 0)
print(arr)

medium

A. No error; output is array('i', [0, 1, 2, 3])

B. Error: insert method not available for array; use arr = array.array('i', [0]) + arr

C. Error: insert index out of range; use append instead

D. Error: arrays are immutable; convert to list first

Solution

1. Step 1: Check if array supports insert

   Python's array module supports insert(index, value) method.

2. Step 2: Verify code behavior

   Inserting 0 at index 0 adds it at the start. Printing arr shows array with 0 at front.

3. Final Answer:

   No error; output is array('i', [0, 1, 2, 3]) -> Option A

4. Quick Check:

   array.insert works like list.insert [OK]

Hint: array.insert(index, value) works like list insert [OK]

Common Mistakes:

• Assuming arrays lack insert method
• Thinking arrays are immutable
• Confusing insert with append

5. You need to store a large number of floating-point numbers and perform fast random access and iteration. Which data structure is the best choice and why?

hard

A. Array from the array module with type 'f', because it stores floats efficiently and supports fast access

B. Python list, because it supports mixed data types

C. Linked list, because it allows easy insertion and deletion

D. Dictionary, because it allows key-based access

Solution

1. Step 1: Identify requirements

   Need to store many floats, fast random access, and efficient iteration.

2. Step 2: Compare data structures

   Linked lists have slow random access. Python lists store floats but use more memory. Dictionaries are for key-value pairs, not indexed storage.

3. Step 3: Choose array module

   Arrays with type 'f' store floats compactly and allow fast index access and iteration.

4. Final Answer:

   Array from the array module with type 'f', because it stores floats efficiently and supports fast access -> Option A

5. Quick Check:

   Efficient float storage + fast access = array('f') [OK]

Hint: Use array('f') for efficient float storage and fast access [OK]

Common Mistakes:

• Choosing linked list for fast access
• Using dictionary for indexed data
• Ignoring memory efficiency