dsa-competitive-programming/leetcode/lc1009.cpp

class Solution{
    public : 
        int bitwiseComplement(int n ){
            if(n==0) return 1;
            short c  = bit_width(static_cast<unsigned int>(n));
            int x = (1<<c) -1;
            return ~n&x;

        }
};
/*
Idea:
Flip only the bits used in n's binary representation.

1. Find number of bits in n using:
   std::bit_width(n)
   It returns how many bits are needed to represent n.

2. Create a mask with all those bits set to 1:
   mask = (1 << bit_width) - 1
   Example: bit_width = 3 -> mask = 111

3. Flip n using ~n, then remove extra leading 1s:
   result = (~n) & mask

Special case: n = 0 -> answer = 1
*/