Set Clear Toggle a Specific Bit in DSA Typescript - Practice Problems & Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output after setting the 2nd bit of 8?

Given the number 8 (binary 1000), what is the output after setting the 2nd bit (0-based from right)?

DSA Typescript

let num = 8;
let bitPosition = 2;
num = num | (1 << bitPosition);
console.log(num);

A 14

B 10

C 12

D 8

💡 Hint

Remember, setting a bit means making sure that bit is 1 using OR operation.

8 in binary is 1000. Setting the 2nd bit (counting from 0) means setting the bit for 4 (2^2). 1000 OR 0100 = 1100 which is 12 in decimal.

❓ Predict Output

intermediate

What is the output after clearing the 3rd bit of 15?

Given the number 15 (binary 1111), what is the output after clearing the 3rd bit (0-based from right)?

DSA Typescript

let num = 15;
let bitPosition = 3;
num = num & ~(1 << bitPosition);
console.log(num);

A 8

B 7

C 15

D 11

💡 Hint

Clearing a bit means making that bit 0 using AND with NOT mask.

15 in binary is 1111. Clearing the 3rd bit (bit for 8) means 1111 AND 0111 = 0111 which is 7 in decimal.

❓ Predict Output

advanced

What is the output after toggling the 1st bit of 10?

Given the number 10 (binary 1010), what is the output after toggling the 1st bit (0-based from right)?

DSA Typescript

let num = 10;
let bitPosition = 1;
num = num ^ (1 << bitPosition);
console.log(num);

A 8

B 11

C 10

D 14

💡 Hint

Toggling flips the bit: 0 to 1 or 1 to 0 using XOR.

10 in binary is 1010. Toggling the 1st bit (bit for 2) flips it from 1 to 0: 1010 XOR 0010 = 1000 which is 8 in decimal.

❓ Predict Output

advanced

What is the output after toggling the 0th bit of 7?

Given the number 7 (binary 0111), what is the output after toggling the 0th bit (0-based from right)?

DSA Typescript

let num = 7;
let bitPosition = 0;
num = num ^ (1 << bitPosition);
console.log(num);

A 6

B 5

C 7

D 3

💡 Hint

Toggle flips the bit at the given position.

7 in binary is 0111. Toggling the 0th bit flips it from 1 to 0: 0111 XOR 0001 = 0110 which is 6 in decimal.

🧠 Conceptual

expert

Which operation correctly clears the 4th bit of a number n?

You want to clear (set to 0) the 4th bit (0-based from right) of a number n. Which of the following expressions correctly does this?

A n | (1 << 4)

B ~n & (1 << 4)

C n ^ (1 << 4)

D n & ~(1 << 4)

💡 Hint

Clearing a bit uses AND with the NOT of the bit mask.

To clear a bit, you AND the number with the inverse of the bit mask. Option D does this correctly.

Option D sets the bit, C toggles it, and D is incorrect logic.

Practice

1. What does the operation num | (1 << pos) do to the bit at position pos in the number num?

easy

A. Toggles the bit at position pos

B. Clears the bit at position pos to 0

C. Checks if the bit at position pos is 1

D. Sets the bit at position pos to 1

Solution

1. Step 1: Understand bitwise OR with shifted 1

   The expression 1 << pos creates a number with only the bit at position pos set to 1.

2. Step 2: Apply OR operation to set bit

   Using num | (1 << pos) sets the bit at pos to 1 without changing other bits.

3. Final Answer:

   Sets the bit at position pos to 1 -> Option D

4. Quick Check:

   Bitwise OR with 1 at pos sets bit [OK]

Hint: Use OR with shifted 1 to set a bit [OK]

Common Mistakes:

• Confusing set with clear operation
• Using AND instead of OR to set bit
• Thinking it toggles the bit

2. Which of the following TypeScript code snippets correctly clears (sets to 0) the bit at position pos in the variable num?

easy

A. num = num & (1 << pos);

B. num = num & ~(1 << pos);

C. num = num | (1 << pos);

D. num = num ^ (1 << pos);

Solution

1. Step 1: Understand clearing a bit

   To clear a bit, we AND the number with a mask that has 0 at the target bit and 1s elsewhere.

2. Step 2: Create mask with NOT operator

   ~(1 << pos) creates a mask with 0 at pos and 1s elsewhere, so num & ~(1 << pos) clears the bit.

3. Final Answer:

   num = num & ~(1 << pos); -> Option B

4. Quick Check:

   AND with NOT mask clears bit [OK]

Hint: Use AND with NOT shifted 1 to clear bit [OK]

Common Mistakes:

• Using OR instead of AND to clear bit
• Forgetting to negate the mask
• Using XOR which toggles instead of clears

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

let num = 10; // binary 1010
let pos = 1;
num = num ^ (1 << pos);
console.log(num);

medium

A. 8

B. 10

C. 12

D. 14

Solution

1. Step 1: Understand initial values and bit positions

   Number 10 in binary is 1010. Bit positions (0-based) from right: pos 0=0, pos 1=1, pos 2=0, pos 3=1.

2. Step 2: Apply XOR to toggle bit at position 1

   1 << 1 is 2 (binary 0010). XOR toggles bit 1: 1010 ^ 0010 = 1000 (binary), which is 8 decimal.

3. Final Answer:

   8 -> Option A

4. Quick Check:

   Toggle bit 1 in 10 gives 8 [OK]

Hint: XOR toggles bit; toggle 1 in 1010 gives 1000 (8) [OK]

Common Mistakes:

• Confusing XOR with OR or AND
• Miscounting bit positions
• Assuming toggle sets bit always to 1

4. The following TypeScript code is intended to toggle the bit at position pos in num. What is the error?

let num = 5; // binary 0101
let pos = 2;
num = num & (1 << pos);
console.log(num);

medium

A. It only keeps the bit at pos and clears others

B. It clears the bit instead of toggling

C. It sets the bit instead of toggling

D. It causes a syntax error

Solution

1. Step 1: Analyze the operation used

   The code uses num & (1 << pos), which ANDs num with a mask having 1 only at pos.

2. Step 2: Understand effect of AND with mask

   This operation keeps only the bit at pos and clears all other bits, not toggling the bit.

3. Final Answer:

   It only keeps the bit at pos and clears others -> Option A

4. Quick Check:

   AND with mask keeps only that bit [OK]

Hint: AND with mask keeps only that bit, doesn't toggle [OK]

Common Mistakes:

• Confusing AND with XOR for toggling
• Expecting toggle but using AND
• Ignoring effect on other bits

5. You have a number num = 29 (binary 11101). You want to toggle the bits at positions 0, 2, and 4 simultaneously. Which TypeScript code correctly does this?

hard

A. num = num | ((1 << 0) & (1 << 2) & (1 << 4));

B. num = num & ~((1 << 0) | (1 << 2) | (1 << 4));

C. num = num ^ ((1 << 0) | (1 << 2) | (1 << 4));

D. num = num ^ (1 << 0) & (1 << 2) & (1 << 4);

Solution

1. Step 1: Create mask for bits 0, 2, and 4

   Using OR to combine shifted bits: (1 << 0) | (1 << 2) | (1 << 4) creates mask 10101 binary (decimal 21).

2. Step 2: Use XOR to toggle bits

   XOR with this mask toggles bits 0, 2, and 4 in num.

3. Final Answer:

   num = num ^ ((1 << 0) | (1 << 2) | (1 << 4)); -> Option C

4. Quick Check:

   XOR with combined mask toggles multiple bits [OK]

Hint: Combine bits with OR, toggle with XOR [OK]

Common Mistakes:

• Using AND or OR instead of XOR to toggle
• Using AND between shifted bits instead of OR
• Not combining bits before toggling