Check if Number is Power of Two in DSA Typescript - 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 Typescript

function isPowerOfTwo(n: number): boolean {
  return n > 0 && (n & [1]) === 0;
}

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

An - 1

B1

Cn + 1

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using n + 1 instead of n - 1

Checking n & 1 which only checks if n is odd

Not checking if n is greater than zero

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 Typescript

function isPowerOfTwo(n: number): boolean {
  if ([1]) return false;
  return (n & (n - 1)) === 0;
}

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

An === 0

Bn === 1

Cn <= 0

Dn < 0

Attempts:

3 left

💡 Hint

Common Mistakes

Only checking for zero but not negative numbers

Checking if n === 1 which is a power of two

Using n < 0 which misses zero

Numbers less than or equal to zero cannot be powers of two.

3fill in blank

hard

Fix the error in the bitwise check to correctly identify powers of two.

DSA Typescript

function isPowerOfTwo(n: number): boolean {
  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

Comparing to 1 instead of 0

Using n + 1 instead of n - 1

Not checking if n is positive

The correct check is (n & (n - 1)) === 0.

4fill in blank

hard

Fill both blanks to create a function that returns true if n is a power of two, false otherwise.

DSA Typescript

function isPowerOfTwo(n: number): boolean {
  return n [1] 0 && (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 less than zero instead of greater than zero

Using addition instead of subtraction

Not combining both conditions

The function checks if n is greater than zero and uses n & (n - 1) to verify power of two.

5fill in blank

hard

Fill all three blanks to create a function that returns true if n is a power of two, false otherwise.

DSA Typescript

function isPowerOfTwo(n: number): boolean {
  if (n [1] 0) return false;
  return (n & (n [2] 1)) [3] 0;
}

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

A<=

B-

C===

D>

Attempts:

3 left

💡 Hint

Common Mistakes

Using greater than zero in the if condition

Using addition instead of subtraction

Using assignment (=) instead of comparison (===)

The function returns false if n is less than or equal to zero, then checks if n & (n - 1) === 0.

Practice

1. What does it mean if a number is a power of two?

easy

A. It is divisible by 3

B. It is always an odd number

C. It can be written as 2 raised to some integer exponent

D. It is a prime number

Solution

1. Step 1: Understand the definition of power of two

   A number is a power of two if it equals 2 raised to an integer exponent, like 2^0=1, 2^1=2, 2^2=4, etc.

2. Step 2: Check other options

   Odd numbers, divisibility by 3, or primality do not define powers of two.

3. Final Answer:

   It can be written as 2 raised to some integer exponent -> Option C

4. Quick Check:

   Power of two = 2^n [OK]

Hint: Power of two means 2 multiplied by itself n times [OK]

Common Mistakes:

• Thinking all powers of two are odd
• Confusing powers of two with prime numbers
• Assuming divisibility by 3 means power of two

2. Which of the following TypeScript expressions correctly checks if a number n is a power of two using bitwise operations?

easy

A. return n > 0 && (n & (n - 1)) === 0;

B. return n > 0 && (n | (n - 1)) === 0;

C. return n > 0 && (n & (n + 1)) === 0;

D. return n > 0 && (n ^ (n - 1)) === 0;

Solution

1. Step 1: Understand the bitwise check for power of two

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

2. Step 2: Analyze each option

   return n > 0 && (n & (n - 1)) === 0; uses the correct bitwise AND with (n-1). Options A, B, and C use incorrect bitwise operators or operands.

3. Final Answer:

   return n > 0 && (n & (n - 1)) === 0; -> Option A

4. Quick Check:

   Bitwise AND with (n-1) = 0 means power of two [OK]

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

Common Mistakes:

• Using bitwise OR instead of AND
• Using (n + 1) instead of (n - 1)
• Forgetting to check n > 0

3. What will be the output of this TypeScript code?

function isPowerOfTwo(n: number): boolean {
  return n > 0 && (n & (n - 1)) === 0;
}
console.log(isPowerOfTwo(16));
console.log(isPowerOfTwo(18));

medium

A. true true

B. false true

C. false false

D. true false

Solution

1. Step 1: Check isPowerOfTwo(16)

   16 in binary is 10000. 16 & 15 (01111) = 0, so returns true.

2. Step 2: Check isPowerOfTwo(18)

   18 in binary is 10010. 18 & 17 (10001) = 16 (not zero), so returns false.

3. Final Answer:

   true false -> Option D

4. Quick Check:

   16 is power of two, 18 is not [OK]

Hint: Check bitwise AND with (n-1) to confirm power of two [OK]

Common Mistakes:

• Assuming 18 is power of two because it's even
• Ignoring the n > 0 condition
• Misreading bitwise AND results

4. Identify the error in this TypeScript function that checks if a number is a power of two:

function checkPower(n: number): boolean {
  return (n & (n - 1)) === 0;
}

medium

A. Missing check for n > 0 to avoid false positives

B. Incorrect bitwise operator used

C. Function should return number, not boolean

D. Parentheses are misplaced

Solution

1. Step 1: Analyze the function logic

   The function uses bitwise AND correctly but does not check if n is positive.

2. Step 2: Understand why n > 0 is needed

   Without n > 0, input 0 returns true incorrectly because 0 & -1 = 0.

3. Final Answer:

   Missing check for n > 0 to avoid false positives -> Option A

4. Quick Check:

   Check n > 0 before bitwise test [OK]

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

Common Mistakes:

• Ignoring zero or negative inputs
• Assuming bitwise alone is enough
• Misunderstanding bitwise AND behavior

5. You want to filter an array of numbers to keep only those that are powers of two. Which TypeScript code snippet correctly does this?

const numbers = [0, 1, 2, 3, 4, 5, 8, 16, 18];
const powersOfTwo = numbers.filter(n => ???);
console.log(powersOfTwo);

hard

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

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

C. n > 0 && (n & (n + 1)) === 0

D. n !== 0 && (n ^ (n - 1)) === 0

Solution

1. Step 1: Understand the filter condition

   We want to keep numbers that are powers of two, so the condition must check n > 0 and bitwise AND with (n-1) equals zero.

2. Step 2: Evaluate each option

   n > 0 && (n & (n - 1)) === 0 correctly uses the standard power of two check. Options B, C, and D use incorrect bitwise operations or conditions.

3. Final Answer:

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

4. Quick Check:

   Filter with bitwise AND and n > 0 [OK]

Hint: Filter with n > 0 and n & (n-1) === 0 [OK]

Common Mistakes:

• Using bitwise OR or XOR instead of AND
• Not checking n > 0
• Using (n + 1) instead of (n - 1)