https://www.acmicpc.net/problem/2606
#include <iostream>
#include <queue>
using namespace std;
int computer[101][101] = { 0, };
int visited[101] = { 0, };
int N, M;
int cnt = 0;
void BFS()
{
queue<int> q;
q.push(1);
visited[1] = 1;
int idx;
while (!q.empty())
{
idx = q.front();
q.pop();
for (int i = 1; i <= N; i++)
{
if (computer[idx][i] == 1 && visited[i] == 0)
{
visited[i] = 1;
q.push(i);
cnt++;
}
}
}
}
int main(void)
{
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
int tmp1, tmp2;
cin >> N >> M;
for (int i = 0; i < M; i++)
{
cin >> tmp1 >> tmp2;
computer[tmp1][tmp2] = 1;
computer[tmp2][tmp1] = 1;
}
BFS();
cout << cnt;
return 0;
}