Array Traversal Patterns in DSA Python - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to print all elements in the array using a for loop.

DSA Python

arr = [10, 20, 30, 40]
for [1] in arr:
    print([1])

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

Ax

Bi

Citem

Dval

Attempts:

3 left

💡 Hint

Common Mistakes

Using an index variable instead of the element variable.

Using different variable names in the loop and print statement.

The variable x is used to represent each element in the array during traversal.

2fill in blank

medium

Complete the code to print elements at even indices of the array.

DSA Python

arr = [5, 10, 15, 20, 25]
for i in range(0, len(arr), [1]):
    print(arr[i])

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A1

B2

C3

D4

Attempts:

3 left

💡 Hint

Common Mistakes

Using step size 1 which prints all elements.

Using step size 3 or 4 which skips too many elements.

Using a step of 2 in range allows traversal of even indices: 0, 2, 4, ...

3fill in blank

hard

Fix the error in the code to print elements in reverse order.

DSA Python

arr = [1, 2, 3, 4, 5]
for i in range(len(arr)-1, [1], -1):
    print(arr[i])

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

A1

B0

C-1

Dlen(arr)

Attempts:

3 left

💡 Hint

Common Mistakes

Using 0 as stop which excludes index 0.

Using len(arr) which is out of range.

The stop value in range is exclusive, so to include index 0 when traversing backwards, use -1 as stop. This generates indices 4, 3, 2, 1, 0.

4fill in blank

hard

Fill both blanks to create a dictionary with elements as keys and their indices as values.

DSA Python

arr = ['a', 'b', 'c']
index_map = [1] for [2] in range(len(arr))}

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A{arr[i]: i

Barr[i]

Ci

Drange(len(arr))

Attempts:

3 left

💡 Hint

Common Mistakes

Using the element as the loop variable instead of the index.

Swapping key and value in the dictionary.

The dictionary comprehension uses {arr[i]: i for i in range(len(arr))} to map elements to indices.

5fill in blank

hard

Fill all three blanks to create a list of squares of even numbers from the array.

DSA Python

arr = [1, 2, 3, 4, 5, 6]
squares = [[1] for [2] in arr if [3] % 2 == 0]

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Ax**2

Bx

Dnum

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variable names in the loop and condition.

Not squaring the variable in the output expression.

The list comprehension squares each x in arr only if x is even.