b2.cpp

#include <iostream>
#include <vector>
#include <algorithm>

int main()
{
	size_t n = 0;
	size_t count = 0;
	while(std::cin >> n) {
		std::vector<size_t> vec(n);
		for(auto & v : vec) cin >> v;

		std::sort(vec.begin(), vec.end());

		std::set<size_t> s;
		bool good = true;
		for(size_t i=0;i<n;i++) {
			size_t a = vec[i];
			for(size_t j=i;j<n;j++) {
				size_t b = vec[j];
				//std::cout << i << " " << j << " " << a+b << std::endl;
				if(s.find(a+b) != s.end()) {
					good = false;
					break;
				}
				s.insert(a+b);
			}
			if(good == false) break;
		}

		if(good)
			std::cout << "Case #" << count <<": It is a B2-Sequence.\n\n";
		else
			std::cout << "Case #" << count << ": It is not a B2-Sequence.\n\n";
	}
}