A plain Bloom filter can never remove an item, because clearing a bit might erase some other item sharing it. The counting Bloom filter fixes this by replacing each bit with a small counter. Today you build that array and its Add.
Build a counting filter whose Add increments the k counters, and whose Contains checks all k are above zero.
The plain Bloom filter has no Delete, and for a good reason: a bit might be set by several items at once, so clearing it to remove one item would silently remove the others too. The counting Bloom filter trades a little more space for the ability to delete. Instead of one bit per slot it keeps a small counter, and Add increments the k counters rather than just setting bits.
Contains follows the same “all k must agree” rule as before, now phrased over counters: an item is possibly present only if every one of its k counters is above zero. With a single "cat" added, its three counters sit at 1 and membership works exactly like the bit version. The payoff arrives next lesson, when a nonzero counter lets us subtract an item back out without disturbing its neighbours.
type Counting struct {counts []uint8m, k int}func NewCounting(m, k int) *Counting { return &Counting{counts: make([]uint8, m), m: m, k: k} }func (f *Counting) Add(data []byte) { /* increment each of the k indices */ }func (f *Counting) Contains(data []byte) bool { /* true if all k counts > 0 */ }