Check if Number is Prime in DSA Python - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check if a number is prime by testing divisibility starting from 2.

DSA Python

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

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Anum

Bnum + 1

Cnum // 2 + 1

Dint(num ** 0.5) + 1

Attempts:

3 left

💡 Hint

Common Mistakes

Using num + 1 includes num itself, incorrectly returning False for primes.

Using int(num ** 0.5) + 1 is an optimization but not for this easy task.

The loop must check divisors from 2 up to num (exclusive) to find any divisor. Using num ensures the loop checks up to num-1.

2fill in blank

medium

Complete the code to optimize prime check by testing divisors only up to the square root of the number.

DSA Python

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

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Anum // 2

Bnum

Cint(num ** 0.5) + 1

Dnum // 3

Attempts:

3 left

💡 Hint

Common Mistakes

Checking up to num wastes time.

Using num // 2 is less efficient.

Checking divisors only up to the square root of num is enough to determine primality efficiently.

3fill in blank

hard

Fix the error in the code to correctly check if a number is prime by returning False immediately when a divisor is found.

DSA Python

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

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A%

B//

C*

D==

Attempts:

3 left

💡 Hint

Common Mistakes

Using == instead of % causes a syntax error.

Using // or * does not check divisibility.

The modulo operator % checks if num is divisible by i with no remainder, which means i is a divisor.

4fill in blank

hard

Fill both blanks to create a dictionary comprehension that maps numbers to True if prime, False otherwise, for numbers 2 to 10.

DSA Python

primes = {num: is_prime(num) for num in [1] if num [2] 1}

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Arange(2, 11)

Brange(1, 11)

C>

D>=

Attempts:

3 left

💡 Hint

Common Mistakes

Using range(1, 11) includes 1 which is not prime.

Using >= includes 1 which is not prime.

We want numbers from 2 to 10, so range(2, 11) is correct. The condition num > 1 filters numbers greater than 1.

5fill in blank

hard

Fill all three blanks to create a list comprehension that lists all prime numbers between 10 and 20.

DSA Python

prime_numbers = [[1] for n in [2] if is_prime([3])]

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An

Brange(10, 21)

Drange(11, 20)

Attempts:

3 left

💡 Hint

Common Mistakes

Using range(11, 20) excludes 10 and 20.

Using different variables in the comprehension causes errors.

The list comprehension iterates over numbers 10 to 20 inclusive using range(10, 21), checks if each number n is prime, and collects n if true.