洛谷

DFS

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

const int MAXN = 10005;
vector<int> adj[MAXN];
bool visited[MAXN];

void dfs(int u) {
    visited[u] = true;
    for (int v : adj[u])
        if (!visited[v])
            dfs(v);
}

int main() {
    int n, m, u, v, count = 0;
    cin >> n >> m;

    // 初始化访问标记
    for (int i = 1; i <= n; i++)
        visited[i] = false;

    // 读入边
    while (m--) {
        cin >> u >> v;
        adj[u].push_back(v);
        adj[v].push_back(u);
    }

    // 统计连通分量
    for (int i = 1; i <= n; i++)
        if (!visited[i]) {
            dfs(i);
            count++;
        }

    cout << "连通分量数: " << count << endl;
    return 0;
}