Question

I am looking for a standard container/library in C++ with following functionalities:

1. Storing the windows of numbers (enqueue and dequeue are enough).
2. Returning the number of unique numbers in the window.

It can be something merging std::queue and std::set capabilities.

EDITED:
Example expected operation. For this sequence ‘1 2 3 3 4 4 5 5 6 6 7 7 8’ and window size of 2 we would have following steps:

1. Window = [1 2], unique ones = 2
2. Window = [2 3], unique ones = 2
3. Window = [3 3], unique ones = 1
4. Window = [3 4], unique ones = 2
5. and so on …

Answer 1

You want two containers:

• a deque<number> to store the numbers in the window in order;
• a map<number, size_t> (or unordered_map if available) to store the count of each unique number.

Then your operations are:

void push(number n) {
    deque.push_back(n);
    ++map[n];
}

void pop() {
    auto found = map.find(deque.front());
    assert(found != map.end());
    assert(found->second > 0);
    if (--found->second == 0) {
        map.erase(found);
    }
    deque.pop_front();
}

size_t count_unique() {
    return map.size();
}