无向图的连通分量

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

const int NIL = -1;

vector<int> G[100005];
int n, m;
int color[100005];

void dfs(int r, int id)
{
    stack<int> s;
    s.push(r);
    color[r] = id;

    while (!s.empty())
    {
        int u = s.top();
        s.pop();
        for (int x : G[u])
        {
            if (color[x] == NIL)
            {
                s.push(x);
                color[x] = id;
            }
        }
    }
}

int main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);

    cin >> n >> m;

    for (int i = 0; i < m; ++i)
    {
        int s, t;
        cin >> s >> t;
        G[s].push_back(t);
        G[t].push_back(s);
    }

    int id = 1;
    for (int i = 0; i < n; ++i)
        color[i] = NIL;

    for (int u = 0; u < n; ++u)
    {
        if (color[u] == NIL)
        {
            dfs(u, id++);
        }
    }

    int q;
    cin >> q;
    for (int i = 0; i < q; ++i)
    {
        int s, t;
        cin >> s >> t;
        if (color[s] == color[t])
            cout << "yes" << endl;
        else
            cout << "no" << endl;
    }
}