[백준/2606] 바이러스

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

2606번: 바이러스

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

using namespace std;

vector<int> a[101];
bool check[101];


void dfs(int start) {
	check[start] = true;
	for (int i = 0; i < a[start].size(); i++) {
		if (!check[a[start][i]]) {
			dfs(a[start][i]);
		}
	}
}


int main() {
	int n, m;
	cin >> n >> m;

	for (int i = 0; i < m; i++) {
		int u, v;
		cin >> u >> v;
		a[u].push_back(v);
		a[v].push_back(u);
	}
	for (int i = 1; i <= n; i++) {
		sort(a[i].begin(), a[i].end());
	}

	dfs(1);
	int cnt = 0;
	for (int i = 2; i <= n; i++) {
		if (check[i]) {
			cnt++;
		}
	}
	cout << cnt;
	return 0;
}