Question

I have an interesting bitmask puzzle problem I need help solving in something. Here is the problem:

11010

Each bit represents a characteristic of a piece of content. It is stored in Redis. But to query it, we need every combination so that we can pull up the key. So 11010 would yield these combinations:

11010
10000
10010
11000
01010
00010
01000

Anyone have a solution in C++?

Answer 1

See the Chess Programming Wiki for an algorithm that is linear in the number of subsets of the initial bitmask. With n bits set to 1, that number is equal to 2^n, so it’s exponential in the number of set bits.

// enumerate all subsets of set d
void enumerateAllSubsets(U64 d) {
   U64 n = 0;
   do {
      doSomeThingWithSubset(n);
      n = (n - d) & d;
   } while ( n );
}