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

func isPowerOfTwo(n int) bool {
    return n > 0 && (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

Not checking if n is greater than zero

The expression n & (n-1) clears the lowest set bit. If the result is zero, n is a power of two.

2fill in blank

medium

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

DSA Go

func isPowerOfTwo(n int) bool {
    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 zero but not negative numbers

Returning true for zero or negative numbers

Numbers less than or equal to zero cannot be powers of two, so we return false for n <= 0.

3fill in blank

hard

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

DSA Go

func isPowerOfTwo(n int) bool {
    if n <= 0 {
        return false
    }
    return (n [1] (n - 1)) == 0
}

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

A&

B<<

C|

D^

Attempts:

3 left

💡 Hint

Common Mistakes

Using bitwise OR or XOR instead of AND

Using shift operators incorrectly

The bitwise AND operator & is used to check if n is a power of two by clearing the lowest set bit.

4fill in blank

hard

Fill both blanks to complete the function that returns true if n is a power of two.

DSA Go

func isPowerOfTwo(n int) bool {
    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 first blank

Using + 1 instead of - 1 in the second blank

The function first checks if n is less than or equal to zero, then uses n & (n - 1) to check if n is a power of two.

5fill in blank

hard

Fill all three blanks to create a map of numbers to booleans indicating if they are powers of two.

DSA Go

func powersMap(nums []int) map[int]bool {
    result := make(map[int]bool)
    for _, [1] := range nums {
        if [2] <= 0 {
            result[[3]] = false
        } else {
            result[[3]] = ([2] & ([2] - 1)) == 0
        }
    }
    return result
}

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

Anum

Bn

Cval

Dx

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variable names in the blanks

Using undefined variables

The loop variable is num. We check if num is positive and then use the bitwise check to set the map value.

Practice

1. Which of the following statements correctly describes a number that is a power of two?

easy

A. It has exactly one bit set to 1 in its binary form.

B. It is always an odd number.

C. It is divisible by 3.

D. It has all bits set to 1 in its binary form.

Solution

1. Step 1: Understand binary representation of powers of two

   A power of two in binary has exactly one '1' bit and the rest are '0's. For example, 4 is 100 in binary.

2. Step 2: Analyze the options

   The statement "It has exactly one bit set to 1 in its binary form" matches the binary property of powers of two. The other options do not: powers of two (except 1) are even, not divisible by 3, and do not have all bits set to 1.

3. Final Answer:

   It has exactly one bit set to 1 in its binary form. -> Option A

4. Quick Check:

   Power of two = one '1' bit [OK]

Hint: Power of two has only one '1' bit in binary [OK]

Common Mistakes:

• Thinking powers of two are always odd
• Confusing powers of two with numbers divisible by 3
• Assuming all bits are set to 1

2. Which of the following Go code snippets correctly checks if an integer n is a power of two?

easy

A. if n & (n + 1) == 0 { /* power of two */ }

B. if n | (n - 1) == 0 { /* power of two */ }

C. if n & (n - 1) == 0 { /* power of two */ }

D. if n ^ (n - 1) == 0 { /* power of two */ }

Solution

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

   The expression n & (n - 1) == 0 is true only if n is a power of two (and n > 0).

2. Step 2: Analyze each option

   The snippet if n & (n - 1) == 0 { /* power of two */ } uses the correct bitwise AND operation. The others use incorrect bitwise operations that do not correctly check for power of two.

3. Final Answer:

   if n & (n - 1) == 0 { /* power of two */ } -> Option C

4. Quick Check:

   Use n & (n-1) == 0 to check 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
• Using XOR which does not work here

3. What is the output of the following Go code?

package main
import "fmt"
func main() {
    n := 16
    if n > 0 && (n & (n - 1)) == 0 {
        fmt.Println("Power of Two")
    } else {
        fmt.Println("Not Power of Two")
    }
}

medium

A. Runtime Error

B. Power of Two

C. Compilation Error

D. Not Power of Two

Solution

1. Step 1: Evaluate the condition for n = 16

   16 in binary is 10000. 16 - 1 = 15 (binary 01111). Bitwise AND: 10000 & 01111 = 0.

2. Step 2: Check the if condition

   Since n > 0 and bitwise AND is 0, the condition is true, so it prints "Power of Two".

3. Final Answer:

   Power of Two -> Option B

4. Quick Check:

   16 & 15 == 0 means power of two [OK]

Hint: Check if n & (n-1) == 0 and n > 0 [OK]

Common Mistakes:

• Ignoring n > 0 check
• Misunderstanding bitwise AND result
• Assuming all even numbers are powers of two

4. The following Go code is intended to check if n is a power of two. What is the error?

func isPowerOfTwo(n int) bool {
    return n & (n - 1) == 0
}

medium

A. The function should return an integer, not bool.

B. The bitwise AND operator is used incorrectly.

C. The parentheses around n - 1 are unnecessary and cause error.

D. It does not handle the case when n is zero or negative.

Solution

1. Step 1: Understand the function logic

   The expression n & (n - 1) == 0 returns true for powers of two and also for zero.

2. Step 2: Identify missing check

   Zero and negative numbers are not powers of two, but this function returns true for zero. It lacks a check for n > 0.

3. Final Answer:

   It does not handle the case when n is zero or negative. -> Option D

4. Quick Check:

   Check n > 0 before bitwise test [OK]

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

Common Mistakes:

• Not checking for n > 0
• Misusing bitwise operators
• Assuming parentheses cause error

5. You want to write a Go function that returns true if a number n is a power of two, but also handles zero and negative inputs correctly. Which of the following implementations is correct?

hard

A. func isPowerOfTwo(n int) bool {
return n > 0 && (n & (n - 1)) == 0
}

B. func isPowerOfTwo(n int) bool {
return n >= 0 && (n | (n - 1)) == 0
}

C. func isPowerOfTwo(n int) bool {
return n != 0 && (n & (n + 1)) == 0
}

D. func isPowerOfTwo(n int) bool {
return (n & (n - 1)) == 1
}

Solution

1. Step 1: Check for positive input

   The function must ensure n is greater than zero to exclude zero and negatives.

2. Step 2: Use correct bitwise condition

   The condition (n & (n - 1)) == 0 correctly identifies powers of two.

3. Step 3: Analyze options

   The implementation func isPowerOfTwo(n int) bool { return n > 0 && (n & (n - 1)) == 0 } correctly combines both checks. The others use incorrect operators or conditions.

4. Final Answer:

   func isPowerOfTwo(n int) bool { return n > 0 && (n & (n - 1)) == 0 } -> Option A

5. Quick Check:

   Check n > 0 and n & (n-1) == 0 [OK]

Hint: Check n > 0 and n & (n-1) == 0 for power of two [OK]

Common Mistakes:

• Using bitwise OR instead of AND
• Not checking n > 0
• Using wrong bitwise expressions