백준 1822 C++ 차집합

#include <bits/stdc++.h>
using namespace std;

int main() {
	cin.tie(0)->sync_with_stdio(0);
	int a, b;
	cin >> a >> b;

	set<int> s;
	for (int i = 0, x; i < a; i++) {
		cin >> x;
		s.emplace(x);
	}
	for (int i = 0, x; i < b; i++) {
		cin >> x;
		s.erase(x);

	}
	cout << s.size() << "\n";
	for (auto num : s) {
		cout << num << " ";
	}
	cout << "\n";

	return 0;
}