Check if Number is Power of Two in DSA Python - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check if a number is a power of two using bitwise AND.

DSA Python

def is_power_of_two(n):
    return n > 0 and (n & ([1])) == 0

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

An - 1

Bn + 1

C1

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using n + 1 instead of n - 1

Checking n & 1 which only checks if n is odd

Using 0 instead of n - 1 in the bitwise AND

The expression n & (n - 1) clears the lowest set bit. For powers of two, this results in zero.

2fill in blank

medium

Complete the code to return False immediately if the number is not positive.

DSA Python

def is_power_of_two(n):
    if [1]:
        return False
    return (n & (n - 1)) == 0

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

An == 0

Bn <= 0

Cn < 0

Dn >= 0

Attempts:

3 left

💡 Hint

Common Mistakes

Checking only for n == 0 and missing negative numbers

Using n >= 0 which includes zero and positive numbers

Only positive numbers can be powers of two, so return False if n is zero or negative.

3fill in blank

hard

Fix the error in the code to correctly check if n is a power of two.

DSA Python

def is_power_of_two(n):
    if n <= 0:
        return False
    return (n & ([1])) == 0

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

An - 1

Bn + 1

C1

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using n + 1 instead of n - 1

Using 1 or 0 directly in the bitwise AND

The correct expression is n & (n - 1) to check if n is a power of two.

4fill in blank

hard

Fill both blanks to complete the function that returns True if n is a power of two, else False.

DSA Python

def is_power_of_two(n):
    if n [1] 0:
        return False
    return (n & (n [2] 1)) == 0

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

A<=

B>

C-

D+

Attempts:

3 left

💡 Hint

Common Mistakes

Using > 0 instead of <= 0 in the if condition

Using + 1 instead of - 1 in the bitwise AND

Check if n is less than or equal to zero to return False. Then use n - 1 in the bitwise AND.

5fill in blank

hard

Fill all three blanks to complete the function that checks if a number is a power of two.

DSA Python

def is_power_of_two(n):
    if n [1] 0:
        return False
    return (n [2] (n [3] 1)) == 0

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

A<=

B&

C-

D+

Attempts:

3 left

💡 Hint

Common Mistakes

Using + instead of - in the expression

Using | instead of & for bitwise operation

Checking n < 0 instead of n <= 0

Return False if n is less than or equal to zero. Then use bitwise AND (&) between n and n - 1.

Practice

1. Which of the following numbers is a power of two?

easy

A. 16

B. 18

C. 20

D. 22

Solution

1. Step 1: Understand powers of two

   Powers of two are numbers like 1, 2, 4, 8, 16, 32, etc., where each is 2 raised to an integer.

2. Step 2: Check each option

   16 = 2^4, so it is a power of two. Others like 18, 20, 22 are not powers of two.

3. Final Answer:

   16 -> Option A

4. Quick Check:

   16 = 2^4 [OK]

Hint: Only numbers with one '1' bit in binary are powers of two [OK]

Common Mistakes:

• Confusing even numbers with powers of two
• Thinking any multiple of 2 is a power of two

2. Which of the following Python expressions correctly checks if n is a power of two?

easy

A. n | (n - 1) == 0

B. n & (n - 1) == 0

C. n ^ (n - 1) == 0

D. n + (n - 1) == 0

Solution

1. Step 1: Understand bitwise AND check

   For powers of two, binary form has only one '1'. n & (n-1) clears the lowest set bit. If result is 0, n is power of two.

2. Step 2: Analyze options

   n & (n - 1) == 0 uses correct bitwise AND check. Others use OR, XOR, or addition which do not correctly check power of two.

3. Final Answer:

   n & (n - 1) == 0 -> Option B

4. Quick Check:

   Bitwise AND check is standard for power of two [OK]

Hint: Use n & (n-1) == 0 to check power of two [OK]

Common Mistakes:

• Using OR or XOR instead of AND
• Forgetting to check n > 0 before this test

3. What is the output of the following code?

def is_power_of_two(n):
    return n > 0 and (n & (n - 1)) == 0

print(is_power_of_two(32))
print(is_power_of_two(45))

medium

A. False\nFalse

B. False\nTrue

C. True\nFalse

D. True\nTrue

Solution

1. Step 1: Check 32

   32 is 2^5, so n > 0 and n & (n-1) == 0 is True.

2. Step 2: Check 45

   45 is not a power of two, so n & (n-1) != 0, returns False.

3. Final Answer:

   True\nFalse -> Option C

4. Quick Check:

   32 power of two = True, 45 not = False [OK]

Hint: Check output for known powers of two and non-powers [OK]

Common Mistakes:

• Ignoring n > 0 condition
• Assuming all even numbers are powers of two

4. Find the error in this code snippet that checks if a number is a power of two:

def check_power(n):
    if n & (n - 1) == 0:
        return True
    else:
        return False

print(check_power(0))

medium

A. Missing check for n > 0 before bitwise operation

B. No error, code works fine

C. Should use OR instead of AND

D. Return values should be strings 'True' or 'False'

Solution

1. Step 1: Analyze bitwise check

   n & (n-1) == 0 works only if n > 0. For n=0, it returns True incorrectly.

2. Step 2: Identify missing condition

   Code lacks n > 0 check, so 0 incorrectly returns True.

3. Final Answer:

   Missing check for n > 0 before bitwise operation -> Option A

4. Quick Check:

   Always check n > 0 before bitwise test [OK]

Hint: Always check n > 0 before bitwise power of two test [OK]

Common Mistakes:

• Not handling zero or negative inputs
• Using wrong bitwise operators

5. You want to filter a list to keep only numbers that are powers of two. Which code snippet correctly does this?

nums = [0, 1, 2, 3, 4, 5, 8, 16, 18]

A) result = [x for x in nums if x & (x - 1) == 0]
B) result = [x for x in nums if x > 0 and x & (x - 1) == 0]
C) result = [x for x in nums if x | (x - 1) == 0]
D) result = [x for x in nums if x > 0 or x & (x - 1) == 0]

hard

A. result = [x for x in nums if x & (x - 1) == 0]

B. result = [x for x in nums if x > 0 or x & (x - 1) == 0]

C. result = [x for x in nums if x | (x - 1) == 0]

D. result = [x for x in nums if x > 0 and x & (x - 1) == 0]

Solution

1. Step 1: Understand filtering condition

   We must check x > 0 to avoid zero or negative numbers passing the test.

2. Step 2: Analyze each option

   result = [x for x in nums if x > 0 and x & (x - 1) == 0] correctly uses x > 0 and bitwise check. result = [x for x in nums if x & (x - 1) == 0] misses x > 0, so 0 passes incorrectly. Options C and D use wrong operators or logic.

3. Final Answer:

   result = [x for x in nums if x > 0 and x & (x - 1) == 0] -> Option D

4. Quick Check:

   Filter with x > 0 and bitwise AND check [OK]

Hint: Filter with x > 0 and x & (x-1) == 0 for powers of two [OK]

Common Mistakes:

• Not filtering out zero
• Using OR instead of AND in condition
• Using bitwise OR instead of AND