Why Arrays Exist and What Problem They Solve in DSA Python - Test Your Knowledge

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create an array with 5 elements initialized to zero.

DSA Python

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

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

A0

BNone

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 created with 5 zeros because 0 is used as the initial value.

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'

A3

B1

C2

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.

Array indexing starts at 0, so the third element is at index 2.

3fill in blank

hard

Fix the error in the code to correctly update the second element of the array to 99.

DSA Python

arr = [5, 10, 15]
arr[[1]] = 99
print(arr)

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

A3

B2

C0

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Using index 2 updates the third element, not the second.

Using index 3 causes an index error because the array has only 3 elements.

The second element is at index 1, so arr[1] = 99 updates it correctly.

4fill in blank

hard

Fill both blanks to create an array of squares of numbers from 1 to 5.

DSA Python

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

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

A**

B6

C*

D5

Attempts:

3 left

💡 Hint

Common Mistakes

Using '*' multiplies but does not square the number in this context.

Using 5 as range end excludes the number 5.

Using '**' for power and '6' as the range end (exclusive) creates squares from 1 to 5.

5fill in blank

hard

Fill both blanks to create a dictionary of numbers and their cubes for numbers greater than 2.

DSA Python

cubes = {x: x{BLANK_2}}3 for x in range(1, 6) if x {{BLANK_2}} 2
print(cubes)

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

Ax

B**

C>

D{

Attempts:

3 left

💡 Hint

Common Mistakes

Using '(' instead of '{' will cause a syntax error.

Using '*' instead of '**' will multiply but not cube.

Using '<' instead of '>' will filter wrong numbers.

Using '{' to start the dictionary, '**' for power, and '>' to filter numbers greater than 2 creates the correct dictionary.

Practice

1. Why do arrays exist in programming languages like Python?

easy

A. To store only one item at a time

B. To store multiple items of the same type in a continuous block of memory

C. To perform mathematical calculations automatically

D. To replace all other data structures

Solution

1. Step 1: Understand the purpose of arrays

   Arrays are designed to hold multiple items of the same type together in memory for easy access.

2. Step 2: Compare with other options

   Options B, C, and D do not correctly describe arrays' purpose; arrays do not store single items only, do not perform calculations automatically, and do not replace all data structures.

3. Final Answer:

   To store multiple items of the same type in a continuous block of memory -> Option B

4. Quick Check:

   Arrays store multiple same-type items [OK]

Hint: Arrays group same-type items together for fast access [OK]

Common Mistakes:

• Thinking arrays store different types together
• Believing arrays perform calculations automatically
• Confusing arrays with single variables

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

easy

A. arr = array('int', 1, 2, 3)

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

C. arr = array(int, [1, 2, 3])

D. arr = array('i', [1, 2, 3])

Solution

1. Step 1: Recall array module syntax

   In Python, the array module requires the type code as the first argument, then the list of elements.

2. Step 2: Check each option

   arr = array('i', [1, 2, 3]) matches the correct syntax: array('i', [1, 2, 3]). Others have wrong argument order or types.

3. Final Answer:

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

4. Quick Check:

   array(typecode, list) syntax [OK]

Hint: Type code first, then list in array() [OK]

Common Mistakes:

• Swapping arguments order
• Using 'int' instead of 'i' as type code
• Passing elements as separate arguments

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

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

medium

A. 30

B. 40

C. 20

D. IndexError

Solution

1. Step 1: Understand array indexing

   Arrays in Python are zero-indexed, so arr[2] accesses the third element.

2. Step 2: Identify the element at index 2

   The array elements are [10, 20, 30, 40], so index 2 is 30.

3. Final Answer:

   30 -> Option A

4. Quick Check:

   arr[2] = 30 [OK]

Hint: Remember zero-based indexing in arrays [OK]

Common Mistakes:

• Confusing index 2 with the second element
• Expecting IndexError for valid index
• Mixing up array and list indexing

4. Identify the error in the following code that tries to create an array and append a string:

from array import array
arr = array('i', [1, 2, 3])
arr.append('4')

medium

A. TypeError because '4' is a string, not an integer

B. SyntaxError due to wrong append syntax

C. No error, code runs fine

D. ValueError because '4' is not a valid integer

Solution

1. Step 1: Check array type and append argument

   The array is of type 'i' (integers), but append tries to add a string '4'.

2. Step 2: Understand type mismatch error

   Appending a string to an integer array causes a TypeError in Python.

3. Final Answer:

   TypeError because '4' is a string, not an integer -> Option A

4. Quick Check:

   Appending wrong type causes TypeError [OK]

Hint: Append only matching type elements to arrays [OK]

Common Mistakes:

• Assuming append accepts any type
• Confusing TypeError with ValueError
• Ignoring type code of array

5. You want to store 1000 numbers and access them quickly by index. Why is using an array better than a Python list in this case?

hard

A. Arrays automatically sort the numbers for quick access

B. Lists are always faster and use less memory than arrays

C. Arrays use less memory and provide faster access for same-type data

D. Lists cannot store more than 100 elements

Solution

1. Step 1: Compare memory usage of arrays and lists

   Arrays store same-type data in continuous memory, using less space than lists which store references.

2. Step 2: Consider access speed

   Arrays provide faster access due to memory locality and fixed type, unlike lists which hold references to objects.

3. Step 3: Evaluate other options

   Lists are not always faster or smaller; arrays do not sort automatically; lists can store more than 100 elements.

4. Final Answer:

   Arrays use less memory and provide faster access for same-type data -> Option C

5. Quick Check:

   Arrays = efficient memory + fast access [OK]

Hint: Arrays save memory and speed up access for uniform data [OK]

Common Mistakes:

• Thinking lists are always better
• Believing arrays sort data automatically
• Assuming lists have size limits