Why Math and Number Theory Appear in DSA Problems in DSA Python - Test Your Knowledge

Practice - 5 Tasks

1fill in blank

easy

Complete the code to calculate the greatest common divisor (GCD) of two numbers using Euclid's algorithm.

DSA Python

def gcd(a, b):
    while b != 0:
        a, b = b, a [1] b
    return a

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

A+

B%

C-

D*

Attempts:

3 left

💡 Hint

Common Mistakes

Using subtraction instead of modulo

Using addition or multiplication incorrectly

The modulo operator (%) gives the remainder, which is used in Euclid's algorithm to find the GCD.

2fill in blank

medium

Complete the code to check if a number n is prime by testing divisibility up to its square root.

DSA Python

def is_prime(n):
    if n <= 1:
        return False
    for i in range(2, int(n[1]0.5) + 1):
        if n % i == 0:
            return False
    return True

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

A**

B*

C//

D+

Attempts:

3 left

💡 Hint

Common Mistakes

Using multiplication instead of exponentiation

Using integer division which truncates

Using exponentiation (**) to calculate the square root is common in prime checks.

3fill in blank

hard

Fix the error in the code to compute the modular exponentiation (a^b mod m) efficiently.

DSA Python

def mod_exp(a, b, m):
    result = 1
    a = a % m
    while b > 0:
        if b & 1 == 1:
            result = (result * a) [1] m
        a = (a * a) % m
        b = b >> 1
    return result

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

A+

B-

C*

D%

Attempts:

3 left

💡 Hint

Common Mistakes

Using multiplication without modulo

Using addition or subtraction instead of modulo

The modulo operator (%) ensures the result stays within the modulus after multiplication.

4fill in blank

hard

Fill both blanks to create a dictionary comprehension that maps numbers to their squares only if the number is even.

DSA Python

squares = {x: x[1]2 for x in range(1, 11) if x [2] 2 == 0}

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

A**

B+

C%

D-

Attempts:

3 left

💡 Hint

Common Mistakes

Using addition instead of exponentiation

Using subtraction instead of modulo

Use '**' to square numbers and '%' to check if a number is even (remainder 0).

5fill in blank

hard

Fill all three blanks to create a dictionary comprehension that maps uppercase letters to their ASCII codes only if the code is greater than 65.

DSA Python

ascii_map = { [1]: [2] for [1] in map(chr, range(65, 91)) if ord([3]) > 65 }

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

Aletter

Bord(letter)

Dchar

Attempts:

3 left

💡 Hint

Common Mistakes

Using inconsistent variable names

Using char instead of letter in condition

Use 'letter' as the variable, 'ord(letter)' to get ASCII code, and 'letter' in the condition.