(c++) 백준 "2606) 바이러스"

https://www.acmicpc.net/problem/2606

---

#include <iostream>
#include <vector>
#include <set>
#include <stack>
using namespace std;

int main() {
	int N,M; cin >> N>>M;
	vector<vector<int>> connect(101);
	for (int i = 0; i < M; i++) {
		int a, b; cin >> a >> b;
		connect[a].push_back(b);
		connect[b].push_back(a);
	}
	stack<int> s; s.push(1);
	set<int> sets; 
	while (!s.empty()) {
		int num = s.top(); s.pop();
		sets.insert(num);
		for (int n : connect[num]) {
			if (sets.find(n) == sets.end()) {
				s.push(n);
			}
		}
	}
	cout << sets.size()-1 << endl;
	return 0;
}