What are bit masks and how are they used to represent subsets?

A bit mask is an integer where each bit represents whether a corresponding element is included in a subset. For a set of n elements, an n-bit integer can represent any subset: bit at position i equals one means element i is included. Iterating from zero to two to the power of n minus one enumerates all possible subsets. To check if element i is in the mask, AND the mask with one shifted left by i. To add element i, OR the mask with one shifted left by i. To remove, AND with the complement.