Set Clear Toggle a Specific Bit in DSA Go - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does it mean to set a specific bit in a number?

Setting a specific bit means changing that bit to 1, regardless of its previous value. It is like turning on a light switch at a certain position.

beginner

How do you clear a specific bit in a number?

Clearing a specific bit means changing that bit to 0, no matter what it was before. It is like turning off a light switch at a certain position.

beginner

What does toggle a specific bit mean?

Toggling a bit means changing it from 0 to 1 or from 1 to 0. It flips the bit's value, like flipping a switch.

intermediate

In Go, how do you set the 3rd bit (0-based) of an integer variable n?

Use the bitwise OR operator with 1 shifted left by 3: n = n | (1 << 3). This sets the 3rd bit to 1.

intermediate

How do you clear the 2nd bit of an integer n in Go?

Use bitwise AND with the complement of 1 shifted left by 2: n = n & ^(1 << 2). This clears the 2nd bit to 0.

Which operator is used to set a specific bit in Go?

A Bitwise XOR (^)

B Bitwise AND (&)

C Bitwise OR (|)

D Bitwise NOT (^)

Setting a bit uses bitwise OR to turn that bit on.

How do you clear a bit at position k in Go?

A n = n | (1 << k)

B n = n & ^(1 << k)

C n = n ^ (1 << k)

D n = n & (1 << k)

Clearing a bit uses AND with the complement of the bit mask.

What does toggling a bit do?

A Flips the bit from 0 to 1 or 1 to 0

B Clears the bit to 0

C Sets the bit to 1

D Leaves the bit unchanged

Toggling flips the bit's value.

Which Go expression toggles the bit at position k of n?

A n = n ^ (1 << k)

B n = n | (1 << k)

C n = n & ^(1 << k)

D n = n << k

XOR (^) with the bit mask toggles the bit.

If n = 8 (binary 1000), what is n after setting bit 1?

A 0 (binary 0000)

B 9 (binary 1001)

C 12 (binary 1100)

D 10 (binary 1010)

Setting bit 1 (second bit) changes 1000 to 1010 which is 10.

Explain how to set, clear, and toggle a specific bit in an integer using bitwise operators in Go.

Think about turning bits on, off, or flipping them using masks.

Describe a real-life analogy for setting, clearing, and toggling bits.

Imagine bits as light switches in a room.

Practice

1. What does the operation num |= (1 << 3) do to the number num?

easy

A. Sets the 4th bit of num to 1

B. Clears the 4th bit of num to 0

C. Toggles the 4th bit of num

D. Checks if the 4th bit of num is set

Solution

1. Step 1: Understand bit shifting

   The expression 1 << 3 shifts 1 left by 3 bits, resulting in binary 00001000, which targets the 4th bit.

2. Step 2: Apply bitwise OR to set bit

   Using |= with this mask sets the 4th bit of num to 1 without changing other bits.

3. Final Answer:

   Sets the 4th bit of num to 1 -> Option A

4. Quick Check:

   Set bit = |= (1 << position) [OK]

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

Common Mistakes:

• Confusing set with clear operation
• Using wrong bit position (off by one)
• Thinking it toggles instead of sets

2. Which of the following Go code snippets correctly clears the 2nd bit (bit index 1) of an integer variable num?

easy

A. num &= (1 << 1)

B. num |= (1 << 1)

C. num &= ^(1 << 1)

D. num ^= (1 << 1)

Solution

1. Step 1: Identify clearing operation

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

2. Step 2: Use bitwise AND with negated mask

   ^(1 << 1) creates a mask with all bits 1 except the 2nd bit 0. ANDing clears that bit.

3. Final Answer:

   num &= ^(1 << 1) -> Option C

4. Quick Check:

   Clear bit = &= ^(1 << position) [OK]

Hint: Use AND with negated shifted 1 to clear bit [OK]

Common Mistakes:

• Using OR instead of AND to clear
• Not negating the mask
• Confusing bit index counting

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

package main
import "fmt"
func main() {
    num := 10 // binary 1010
    num ^= (1 << 1)
    fmt.Println(num)
}

medium

A. 10

B. 8

C. 12

D. 14

Solution

1. Step 1: Understand initial value and bit positions

   Number 10 in binary is 1010. Bit positions (0-based) from right: bit0=0, bit1=1, bit2=0, bit3=1.

2. Step 2: Toggle 2nd bit (bit index 1) using XOR

   XOR with (1 << 1) toggles bit1. Bit1 is 1, toggling it changes to 0. New binary: 1000 which is 8.

3. Final Answer:

   8 -> Option B

4. Quick Check:

   Toggle bit = ^= (1 << position) [OK]

Hint: XOR toggles bit: 1->0 or 0->1 [OK]

Common Mistakes:

• Confusing toggle with set or clear
• Misreading bit positions
• Calculating decimal incorrectly

4. The following Go code is intended to clear the 3rd bit (bit index 2) of num. What is the error?

num := 15
num &= (1 << 2)

medium

A. It sets the 3rd bit instead of clearing it

B. No error, it correctly clears the 3rd bit

C. It toggles the 3rd bit instead of clearing

D. It clears all bits except the 3rd bit

Solution

1. Step 1: Analyze the operation performed

   The code does num &= (1 << 2), which ANDs num with 00000100 (only 3rd bit set).

2. Step 2: Understand effect on bits

   This clears all bits except the 3rd bit, effectively keeping only the 3rd bit if it was set, not clearing it.

3. Final Answer:

   It clears all bits except the 3rd bit -> Option D

4. Quick Check:

   Clear bit = &= ^(1 << position) [OK]

Hint: Use AND with negated mask to clear bit [OK]

Common Mistakes:

• Using AND with mask instead of negated mask
• Confusing clear with set or toggle
• Assuming &= (1 << n) clears bit

5. You have an integer num initially 0. You want to toggle the 1st bit, set the 3rd bit, and clear the 2nd bit in this order. Which sequence of operations achieves this correctly in Go?

hard

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

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

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

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

Solution

1. Step 1: Toggle 1st bit (bit 0)

   Use XOR with (1 << 0) to toggle the 1st bit: num ^= (1 << 0).

2. Step 2: Set 3rd bit (bit 2)

   Use OR with (1 << 2) to set the 3rd bit: num |= (1 << 2).

3. Step 3: Clear 2nd bit (bit 1)

   Use AND with negated mask to clear 2nd bit: num &= ^(1 << 1).

4. Final Answer:

   num ^= (1 << 0); num |= (1 << 2); num &= ^(1 << 1) -> Option A

5. Quick Check:

   Toggle, Set, Clear in order with ^=, |=, &= ^ [OK]

Hint: Toggle ^=, Set |=, Clear &= ^ in correct order [OK]

Common Mistakes:

• Mixing order of operations
• Using wrong operators for each action
• Not negating mask when clearing