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Introduction to Bitwise Algorithms – Data Structures and Algorithms Tutorial

Rishabh Prabhu
Published: October 11, 2022

Bit stands for binary digit. A bit is the basic unit of information and can only have one of two possible values that is 0 or 1.

In our world, we usually with numbers using the decimal base. In other words. we use the digit 0 to 9 However, there are other number representations that can be quite useful such as the binary number systems.

Introduction to Bitwise Algorithms - Data Structures and Algorithms Tutorial

Introduction to Bitwise Algorithms – Data Structures and Algorithms Tutorial

Unlike humans, computers have no concepts of words and numbers. They receive data encoded at the lowest level as a series of zeros and ones (0 and 1). These are called bits, and they are the basis for all the commands they receive. We’ll begin by learning about bits and then explore a few algorithms for manipulating bits. We’ll then explore a few algorithms for manipulating bits. The tutorial is meant to be an introduction to bit algorithms for programmers.

Basics of Bit manipulation (Bitwise Operators)

An algorithmic operation known as bit manipulation involves the manipulation of bits at the bit level (bitwise). Bit manipulation is all about these bitwise operations. They improve the efficiency of programs by being primitive, fast actions. 

The computer uses this bit manipulation to perform operations like addition, subtraction, multiplication, and division are all done at the bit level. This operation is performed in the arithmetic logic unit (ALU) which is a part of a computer’s CPU. Inside the ALU, all such mathematical operations are performed.

There are different bitwise operations used in the bit manipulation. These bit operations operate on the individual bits of the bit patterns. Bit operations are fast and can be used in optimizing time complexity. Some common bit operators are:

Bitwise Operator Truth Table

Bitwise Operator Truth Table

1. Bitwise AND Operator (&)

The bitwise AND operator is denoted using a single ampersand symbol, i.e. &. The & operator takes two equal-length bit patterns as parameters. The two-bit integers are compared. If the bits in the compared positions of the bit patterns are 1, then the resulting bit is 1. If not, it is 0.

Truth table of AND operator

Truth table of AND operator

Example: 

Take two bit values X and Y, where X = 7= (111)2 and Y = 4 = (100)2 . Take Bitwise and of both X & y

Bitwise and of 7 & 4

Bitwise ANDof (7 & 4)

Implementation of AND operator:

C++

#include <bits/stdc++.h>

using namespace std;

  

int main()

{

  

    int a = 7, b = 4;

    int result = a & b;

    cout << result << endl;

  

    return 0;

}

2 ​Bitwise OR Operator (|)

The | Operator takes two equivalent length bit designs as boundaries; if the two bits in the looked-at position are 0, the next bit is zero. If not, it is 1.

Truth table of OR operator

Truth table of OR operator

Example: 

Take two bit values X and Y, where X = 7= (111)2 and Y = 4 = (100)2 . Take Bitwise and of both X & y

Bitwise OR of (7 | 4)

Explaination: On the basis of truth table of bitwise OR operator we can conclude that the result of 

1 | 1  = 1
1 | 0 = 1
0 | 1 = 1
0 | 0 = 0

We used the similar concept of bitwise operator that are show in the image.

Implementation of OR operator:

C++

#include <bits/stdc++.h>

using namespace std;

  

int main()

{

  

    int a = 12, b = 25;

    int result = a | b;

    cout << result;

  

    return 0;

}

3. ​Bitwise XOR Operator (^)

The ^ operator (also known as the XOR operator) stands for Exclusive Or. Here, if bits in the compared position do not match their resulting bit is 1. i.e, The result of the bitwise XOR operator is 1 if the corresponding bits of two operands are opposite, otherwise 0.

Truth Table of Bitwise Operator XOR

Truth Table of Bitwise Operator XOR

Example: 

Take two bit values X and Y, where X = 7= (111)2 and Y = 4 = (100)2 . Take Bitwise and of both X & y

Bitwise OR of (7 ^ 4)

Explaination: On the basis of truth table of bitwise XOR operator we can conclude that the result of 

1 ^ 1  = 0
1 ^ 0 = 1
0 ^ 1 = 1
0 ^ 0 = 0

We used the similar concept of bitwise operator that are show in the image.

Implementation of XOR operator:

C++

#include <iostream>

using namespace std;

  

int main()

{

  

    int a = 12, b = 25;

    cout << (a ^ b);

    return 0;

}

4. ​Bitwise NOT Operator (!~)

All the above three bitwise operators are binary operators (i.e, requiring two operands in order to operate). Unlike other bitwise operators, this one requires only one operand to operate.

The bitwise Not Operator takes a single value and returns its one’s complement. The one’s complement of a binary number is obtained by toggling all bits in it, i.e, transforming the 0 bit to 1 and the 1 bit to 0.

Truth Table of Bitwise Operator NOT

Truth Table of Bitwise Operator NOT

Example: 

Take two bit values X and Y, where X = 5= (101)2 . Take Bitwise NOT of X.

 

Explaination: On the basis of truth table of bitwise NOT operator we can conclude that the result of 

~1  = 0
~0 = 1

We used the similar concept of bitwise operator that are show in the image.

Implementation of NOT operator:

C++

#include <iostream>

using namespace std;

  

int main()

{

  

    int a = 0;

    cout << "Value of a without using NOT operator: " << a;

    cout << "\nInverting using NOT operator (with sign bit): " << (~a);

    cout << "\nInverting using NOT operator (without sign bit): " << (!a);

  

    return 0;

}

Output

Value of a without using NOT operator: 0
Inverting using NOT operator (with sign bit): -1
Inverting using NOT operator (without sign bit): 1

5. Left-Shift (<<)

The left shift operator is denoted by the double left arrow key (<<). The general syntax for left shift is shift-expression << k. The left-shift operator causes the bits in shift expression to be shifted to the left by the number of positions specified by k. The bit positions that the shift operation has vacated are zero-filled. 

Note: Every time we shift a number towards the left by 1 bit it multiply that number by 2.

Left-Shift Bitwise Operator

Left-Shift Bitwise Operator

Example:

Input: Left shift of 5 by 1.
Binary representation of 5 = 00101 and Left shift of 001012 by 1 (i.e, 00101 << 1)
 

Left shif of 5 by 1

Output: 10
Explaination: All bit of 5 will be shifted by 1 to left side and this result in 010102, Which is equivalent to 10

Input: Left shift of 5 by 2.
Binary representation of 5 = 00101 and Left shift of 001012 by 1 (i.e, 00101 << 2)

Left shif of 5 by 2

Output: 20
Explaination: All bit of 5 will be shifted by 1 to left side and this result in 101002, Which is equivalent to 20

Input: Left shift of 5 by 3.
Binary representation of 5 = 00101 and Left shift of 001012 by 1 (i.e, 00101 << 3)

Left shif of 5 by 3

Output: 40
Explaination: All bit of 5 will be shifted by 1 to left side and this result in 010002, Which is equivalent to 40

Implementation of Left shift operator:

C++

#include <bits/stdc++.h>

using namespace std;

  

int main()

{

    unsigned int num1 = 1024;

  

    bitset<32> bt1(num1);

    cout << bt1 << endl;

  

    unsigned int num2 = num1 << 1;

    bitset<32> bt2(num2);

    cout << bt2 << endl;

  

    unsigned int num3 = num1 << 2;

    bitset<16> bitset13{ num3 };

    cout << bitset13 << endl;

}

Output

00000000000000000000010000000000
00000000000000000000100000000000
0001000000000000

6. Right-Shift (>>)

The right shift operator is denoted by the double right arrow key (>>). The general syntax for the right shift is “shift-expression >> k”. The right-shift operator causes the bits in shift expression to be shifted to the right by the number of positions specified by k. For unsigned numbers, the bit positions that the shift operation has vacated are zero-filled. For signed numbers, the sign bit is used to fill the vacated bit positions. In other words, if the number is positive, 0 is used, and if the number is negative, 1 is used.

Note: Every time we shift a number towards the right by 1 bit it divides that number by 2.

Right-Shift Operator

Right-Shift Operator

Example:

Input: Left shift of 5 by 1.
Binary representation of 5 = 00101 and Left shift of 001012 by 1 (i.e, 00101 << 1)

Rightshif of 5 by 1

Output: 10
Explaination: All bit of 5 will be shifted by 1 to left side and this result in 010102, Which is equivalent to 10

Input: Left shift of 5 by 2.
Binary representation of 5 = 00101 and Left shift of 001012 by 1 (i.e, 00101 << 2)

Right shif of 5 by 2

Output: 20
Explaination: All bit of 5 will be shifted by 1 to left side and this result in 101002, Which is equivalent to 20

Input: Left shift of 5 by 3.
Binary representation of 5 = 00101 and Left shift of 001012 by 1 (i.e, 00101 << 3)

Right shif of 5 by 3

Output: 40
Explaination: All bit of 5 will be shifted by 1 to left side and this result in 010002, Which is equivalent to 40

Implementation of Right shift operator:

C++

#include <bitset>

#include <iostream>

  

using namespace std;

  

int main()

{

    unsigned int num1 = 1024;

  

    bitset<32> bt1(num1);

    cout << bt1 << endl;

  

    unsigned int num2 = num1 >> 1;

    bitset<32> bt2(num2);

    cout << bt2 << endl;

  

    unsigned int num3 = num1 >> 2;

    bitset<16> bitset13{ num3 };

    cout << bitset13 << endl;

}

Output

00000000000000000000010000000000
00000000000000000000001000000000
0000000100000000

Application of BIT Operators

  • Bit operations are used for the optimization of embedded systems.
  • The Exclusive-or operator can be used to confirm the integrity of a file, making sure it has not been corrupted, especially after it has been in transit.
  • Bitwise operations are used in Data encryption and compression.
  • Bits are used in the area of networking, framing the packets of numerous bits which are sent to another system generally through any type of serial interface.
  • Digital Image Processors use bitwise operations to enhance image pixels and to extract different sections of a microscopic image.

Important Practice Problems on Bitwise Algorithm:

1. How to Set a bit in the number?

If we want to set a bit at nth position in the number ‘num’, it can be done using the ‘OR’ operator( | ).  

  • First, we left shift 1 to n position via (1<<n)
  • Then, use the “OR” operator to set the bit at that position. “OR” operator is used because it will set the bit even if the bit is unset previously in the binary representation of the number ‘num’.

Note: If the bit would be already set then it would remain unchanged.

Below is the implementation:

C++

#include <iostream>

using namespace std;

void set(int& num, int pos)

{

    

    

    num |= (1 << pos);

}

int main()

{

    int num = 4, pos = 1;

    set(num, pos);

    cout << (int)(num) << endl;

    return 0;

}

Java

  

import java.io.*;

  

class GFG {

    public static void main(String[] args)

    {

        int num = 4, pos = 1;

        num = set(num, pos);

        System.out.println(num);

    }

    public static int set(int num, int pos)

    {

        

        

        num |= (1 << pos);

        return num;

    }

}

  

Python3

def set(num, pos):

    

    

    num |= (1 << pos)

    print(num)

  

  

num, pos = 4, 1

  

set(num, pos)

  

C#

using System;

  

public class GFG {

  

    static public void Main()

    {

        int num = 4, pos = 1;

        set(num, pos);

    }

  

    

    

    static public void set(int num, int pos)

    {

        

        

        num |= (1 << pos);

        Console.WriteLine(num);

    }

}

  

Javascript

<script>

function set(num,pos)

{

     

     

     num |= (1 << pos);

     console.log(parseInt(num));

}

  

let num = 4;

let pos = 1;

set(num, pos);

  

  

</script>

2. How to unset/clear a bit at n’th position in the number 

Suppose we want to unset a bit at nth position in number ‘num’ then we have to do this with the help of “AND” (&) operator.

  • First, we left shift ‘1’ to n position via (1<<n) then we use bitwise NOT operator ‘~’ to unset this shifted ‘1’.
  • Now after clearing this left shifted ‘1’ i.e making it to ‘0’ we will ‘AND'(&) with the number ‘num’ that will unset bit at nth position.

Below is the implementation:

C++

#include <iostream>

using namespace std;

void unset(int& num, int pos)

{

    

    

    num &= (~(1 << pos));

}

int main()

{

    int num = 7;

    int pos = 1;

    unset(num, pos);

    cout << num << endl;

    return 0;

}

Java

  

import java.io.*;

  

class GFG {

    public static void main(String[] args)

    {

        int num = 7, pos = 1;

        num = unset(num, pos);

        System.out.println(num);

    }

    public static int unset(int num, int pos)

    {

        

        

        num = num & (~(1 << pos));

        return num;

    }

}

Python3

  

  

def unset(num, pos):

    

    num &= (~(1 << pos))

    print(num)

  

  

num, pos = 7, 1

  

unset(num, pos)

C#

using System;

  

public class GFG {

  

    static public void Main()

    {

        

        

        int num = 7, pos = 1;

        unset(num, pos);

    }

    static public void unset(int num, int pos)

    {

        

        

        num &= (~(1 << pos));

        Console.WriteLine(num);

    }

}

3. Toggling a bit at nth position 

Toggling means to turn bit ‘on'(1) if it was ‘off'(0) and to turn ‘off'(0) if it was ‘on'(1) previously. We will be using the ‘XOR’ operator here which is this ‘^’. The reason behind the ‘XOR’ operator is because of its properties. 

  • Properties of ‘XOR’ operator. 
    • 1^1 = 0
    • 0^0 = 0
    • 1^0 = 1
    • 0^1 = 1
  • If two bits are different then the ‘XOR’ operator returns a set bit(1) else it returns an unset bit(0).

Below is the implementation:

C++

#include <iostream>

using namespace std;

void toggle(int& num, int pos) { num ^= (1 << pos); }

int main()

{

    int num = 4;

    int pos = 1;

    toggle(num, pos);

    cout << num << endl;

    return 0;

}

Java

  

import java.io.*;

  

class GFG {

    public static void main(String[] args)

    {

        int num = 4, pos = 1;

        num = toggle(num, pos);

        System.out.println(num);

    }

    public static int toggle(int num, int pos)

    {

        

        

        num ^= (1 << pos);

        return num;

    }

}

  

Python3

def toggle(num, pos):

    

    

    num ^= (1 << pos)

    print(num)

  

  

num, pos = 4, 1

  

toggle(num, pos)

  

C#

using System;

  

public class GFG {

  

    static public void Main()

    {

        int num = 4, pos = 1;

        toggle(num, pos);

    }

    static public void toggle(int num, int pos)

    {

        

        

        num ^= (1 << pos);

        Console.WriteLine(num);

    }

}

  

4. Checking if the bit at nth position is Set or Unset

We used the left shift (<<) operation on 1 to shift the bits to nth position and then use the & operation with number given number, and check if it is not-equals to 0.

Below is the implementation:

C++

#include <iostream>

using namespace std;

  

bool at_position(int num, int pos)

{

    bool bit = num & (1 << pos);

    return bit;

}

  

int main()

{

    int num = 5;

    int pos = 2;

    bool bit = at_position(num, pos);

    cout << bit << endl;

    return 0;

}

Java

  

import java.io.*;

  

class GFG {

    public static void main(String[] args)

    {

        int num = 5;

        int pos = 0;

        int bit = at_position(num, pos);

        System.out.println(bit);

    }

    public static int at_position(int num, int pos)

    {

        int bit = num & (1 << pos);

        return bit;

    }

}

Python3

def at_position(num, pos):

    bit = num & (1 << pos)

    return bit

  

  

num = 5

pos = 0

bit = at_position(num, pos)

print(bit)

Javascript

<script>

function at_position(num,pos)

{

 return num & (1<<pos);

}

let num = 5;

let pos = 0;

console.log(at_position(num, pos));

</script>

5. Multiply a number by 2 using the left shift operator

Below is the implementation:

C++

#include <iostream>

using namespace std;

int main()

{

    int num = 12;

    int ans = num << 1;

    cout << ans << endl;

    return 0;

}

Java

  

import java.io.*;

  

class GFG {

    public static void main(String[] args)

    {

        int num = 12;

        int ans = num << 1;

        System.out.println(ans);

    }

}

  

C#

using System;

  

public class GFG {

  

    static public void Main()

    {

        int num = 12;

        Console.WriteLine(num << 1);

    }

}

  

Python3

  

num = 12

ans = num << 1

print(ans)

  

Javascript

<script>

  

var num = 12;

var ans = num<<1;

document.write(ans);

  

</script>

6. Divide a number 2 using the right shift operator

Below is the implementation:

C++

#include <iostream>

using namespace std;

int main()

{

    int num = 12;

    int ans = num >> 1;

    cout << ans << endl;

    return 0;

}

Java

  

import java.io.*;

  

class GFG {

    public static void main(String[] args)

    {

        int num = 12;

        int ans = num >> 1;

        System.out.println(ans);

    }

}

  

C#

using System;

  

public class GFG {

  

    static public void Main()

    {

        int num = 12;

        Console.WriteLine(num >> 1);

    }

}

  

Python3

  

num = 12

ans = num >> 1

print(ans)

  

Javascript

<script>

  

var num = 12;

var ans = num>>1;

document.write(ans);

  

</script>

7. Compute XOR from 1 to n (direct method)

The  problem can be solved based on the following observations:

Say x = n % 4. The XOR value depends on the value if x. 

If, x = 0, then the answer is n.
   x = 1, then answer is 1.
   x = 2, then answer is n+1.
   x = 3, then answer is 0.

Below is the implementation of the above approach.

C++

int computeXOR(int n)

{

    if (n % 4 == 0)

        return n;

    if (n % 4 == 1)

        return 1;

    if (n % 4 == 2)

        return n + 1;

    else

        return 0;

}

Java

import java.io.*;

  

class GFG {

  

    

    public static int computeXOR(int n)

    {

        if (n % 4 == 0)

            return n;

        if (n % 4 == 1)

            return 1;

        if (n % 4 == 2)

            return n + 1;

        else

            return 0;

    }

  

    public static void main(String[] args) {}

}

  

Python

def set(num, pos):

  

    

    

num |= (1 << pos)

print(num)

  

num, pos = 4, 1

  

set(num, pos)

  

C#

using System;

public class GFG {

  

    

    public static int computeXOR(int n)

    {

  

        if (n % 4 == 0)

  

            return n;

  

        if (n % 4 == 1)

  

            return 1;

  

        if (n % 4 == 2)

  

            return n + 1;

  

        else

  

            return 0;

    }

    public static void Main() {}

}

  

Javascript

<script>

  

function computeXOR(n)

{

    if (n % 4 == 0)

        return n;

    if (n % 4 == 1)

        return 1;

    if (n % 4 == 2)

        return n + 1;

    else

        return 0;

}

  

  

</script>

8. How to know if a number is a power of 2?

This can be solved based on the following fact:

If a number N is a power of 2, then the bitwise AND of N and N-1 will be 0. But this will not work if N is 0. So just check these two conditions, if any of these two conditions is true.

Below is the implementation of the above approach.

C++

bool isPowerOfTwo(int x)

{

    

    

    return x && (!(x & (x - 1)));

}

Python

def isPowerOfTwo(x):

  

  

    

    

return x and (not(x & (x - 1)))

  

C#

using System;

  

public class GFG {

  

    

    static public bool isPowerOfTwo(int x)

    {

        

        

        return (x != 0) && ((x & (x - 1)) == 0);

    }

  

    static public void Main() {}

}

  

9. Count Set bits in an integer

Counting set bits means, counting total number of 1’s in the binary representation of an integer. For this problem we go through all the bits of given number and check whether it is set or not by performing AND operation (with 1).

Below is the implementation:

C++

int countBits(int n)

{

    

    int count = 0;

    while (n) {

        

        

        count += n & 1;

  

        

        

        

        n >>= 1;

    }

    return count;

}

10. Position of rightmost set bit

The idea is to unset the rightmost bit of number n and XOR the result with n. Then the rightmost set bit in n will be the position of the only set bit in the result. Note that if n is odd, we can directly return 1 as the first bit is always set for odd numbers.

Example: 
The number 20 in binary is 00010100, and the position of the rightmost set bit is 3.

00010100    &               (n = 20)
00010011                     (n-1 = 19)
——————-
00010000    ^                (XOR result number with n)
00010100
——————-
00000100 ——->  rightmost set bit will tell us the position

Below is the implementation:

C++

int positionOfRightmostSetBit(int n)

{

    

    if (n & 1) {

        return 1;

    }

  

    

    n = n ^ (n & (n - 1));

  

    

    

    

    int pos = 0;

    while (n) {

        n = n >> 1;

        pos++;

    }

    return pos;

}

Java

public static int positionOfRightmostSetBit(int n)

{

    

    if ((n & 1) != 0) {

        return 1;

    }

  

    

    n = n ^ (n & (n - 1));

  

    

    

    

    int pos = 0;

    while (n != 0) {

        n = n >> 1;

        pos++;

    }

  

    return pos;

}

Python

  

  

def positionOfRightmostSetBit(n):

  

    if n & 1:

        return 1

  

    

    n = n ^ (n & (n - 1))

  

    

    

    pos = 0

    while n:

        n = n >> 1

        pos = pos + 1

  

    return pos

Related article:

Source: www.geeksforgeeks.org