Bit Manipulation Techniques

Check if a number is even/odd

// Check if number is even
const isEven = (num) => (num & 1) === 0;

// Check if number is odd
const isOdd = (num) => (num & 1) === 1;

This works because the least significant bit is 0 for even numbers and 1 for odd numbers.

Multiplying/Dividing by powers of 2

// Multiply by 2^n
const multiplyByPowerOf2 = (num, n) => num << n;

// Divide by 2^n
const divideByPowerOf2 = (num, n) => num >> n;

// Examples:
const multiplyBy8 = (num) => num << 3;  // num * 8
const divideBy16 = (num) => num >> 4;   // num / 16

Bit shifts are much faster than multiplication and division operations.

Counting set bits (Hamming Weight)

// Simple approach
const countSetBits = (num) => {
  let count = 0;
  while (num > 0) {
    count += num & 1;
    num >>= 1;
  }
  return count;
};

// Brian Kernighan's algorithm (more efficient)
const countSetBitsBK = (num) => {
  let count = 0;
  while (num > 0) {
    num &= (num - 1);  // Clear the least significant set bit
    count++;
  }
  return count;
};

Check if a number is a power of 2

const isPowerOf2 = (num) => {
  // A power of 2 has exactly one bit set
  // Note: this doesn't work for 0
  return num > 0 && (num & (num - 1)) === 0;
};

// Examples:
// 4 (100) & 3 (011) = 0 ✓
// 5 (101) & 4 (100) = 4 ✗

This works because powers of 2 have only one bit set, and subtracting 1 flips all bits from right up to that bit.