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Bitset

Bitset represents a fixed-size sequence of N bits and stores values either 0 or 1. Zero means value is false or bit is unset and one means value is true or bit is set. Bitset class emulates space efficient array of boolean values, where each element occupies only one bit.

As it emulates array, its index also starts from 0th position. Individual bit from bitset can be accessed using subscript operator.
For instance to access first element of bitset test use test[0].

Bitset class provides constructors to create bitset from integer as well as from strings. The size of the bitset is fixed at compile time.

The main function defined for bitset class are operator [], count, size, set, reset and many more they are explained in below code:

int main(){

// default constructor initializes with all bits 0
bitset<32> bset1;

// bset2 is initialized with bits of 20
bitset<32> bset2(20);

// bset3 is initialized with bits of specified binary string
bitset<32> bset3(string("1100"));

// cout prints exact bits representation of bitset
cout << bset1 << endl; // 00000000000000000000000000000000
cout << bset2 << endl; // 00000000000000000000000000010100
cout << bset3 << endl; // 00000000000000000000000000001100

// declaring set8 with capacity of 8 bits

bitset<8> set8; // 00000000

// setting first bit (or 6th index)
set8[1] = 1; // 00000010
set8[4] = set8[1]; // 00010010
cout << set8 << endl; // 00010010

// count function returns number of set bits in bitset
int numberof1 = set8.count();

// size function returns total number of bits in bitset
// so there difference will give us number of unset(0) bits in bitset
int numberof0 = set8.size() - numberof1;

cout << set8 << " has " << numberof1 << " ones and " << numberof0 << " zeros\n";
// 00010010 has 2 ones and 6 zeros

// test function return 1 if bit is set else returns 0
cout << "bool representation of " << set8 << " : ";
for (int i = 0; i < set8.size(); i++)
cout << set8.test(i) << " ";
cout << endl;
// bool representation of 00010010 : 0 1 0 0 1 0 0 0 

// any function returns true, if atleast 1 bit is set
if (!set8.any())
cout << "set8 has no bit set.\n"; // bset1 has no bit set.

// none function returns true, if none of the bit is set
if (!bset1.none())
cout << "bset1 has some bit set\n";

// set() sets all bits
cout << set8.set() << endl; // 11111111

// set(pos, b)
cout << set8.set(4, 0) << endl; // makes set8[4] = 0
// 11101111

// set(pos)
cout << set8.set(4) << endl; // makes set8[4] = 1 i.e. default is 1
// 11111111

// reset function makes all bits 0
cout << set8.reset(2) << endl; // 11111011
cout << set8.reset() << endl; // 00000000

// flip function flips all bits i.e. 1 <-> 0 and 0 <-> 1
cout << set8.flip(2) << endl; // 00000100
cout << set8.flip() << endl; // 11111011

// Converting decimal number to binary by using bitset
int num = 100;
cout << "\nDecimal number: " << num << " Binary equivalent: " << bitset<8>(num);
// Decimal number: 100 Binary equivalent: 01100100

return 0;
}

For bitset all bitwise operator are overloaded that is they can be applied to bitset directly without any casting or conversion, main overloaded operator are &, |, ==, != and shifting operator <> which makes operation on bitset easy.

int main(){ 
bitset<4> bset1(9); // bset1 contains 1001
bitset<4> bset2(3); // bset2 contains 0011

// comparison operator
cout << (bset1 == bset2) << endl; // false 0
cout << (bset1 != bset2) << endl; // true 1

// bitwise operation and assignment
cout << (bset1 ^= bset2) << endl; // 1010
cout << (bset1 &= bset2) << endl; // 0010
cout << (bset1 |= bset2) << endl; // 0011

// left and right shifting
cout << (bset1 <<= 2) << endl; // 1100
cout << (bset1 >>= 1) << endl; // 0110

// not operator
cout << (~bset2) << endl; // 1100

// bitwise operator
cout << (bset1 & bset2) << endl; // 0010
cout << (bset1 | bset2) << endl; // 0111
cout << (bset1 ^ bset2) << endl; // 0101
}

Try the following example in the editor below.

You are given two bitset b1 and b2, perform the operations defined in the comments in the editor below.

Start solving Bitset on Interview Code Editor
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