Bit Operation

n & (n-1): remove the first one

• No. 191: Number of 1 Bits: n & (n-1)

• No. 231: Power of Two: n & (n-1)

• No. 326: Power of Three: Max3PowerInt / this number

• No. 342: Power of Four: ((num-1)&num)==0 && (num-1)%3==0; OR consider 1010101010101010101010101010101 (1431655765)

• No. 2749. Minimum Operations to Make the Integer Zero

  • Many languages offer built-in popcount functions:

    • C++: __builtin_popcountll(x) for long long.

    • Java: Long.bitCount(x).

    • C#: BitOperations.PopCount((ulong)s) (or manual bit counting if unavailable).

    • Python: bin(x).count('1') or use x.bit_count() in Python 3.8+.

  If a built-in is unavailable, implement a small function that counts set bits (e.g., while(x) { count += x & 1; x >>= 1; }).