Go: package main

import (
	"fmt"
	"bufio"
	"os"
	"strconv"
)

func main() {
	var n,m int
	fmt.Scan(&n)
	group := make([]int, n)
	g := make([][]int, n)
	for i := 0; i < n; i++ {
		g[i] = []int{}
		group[i] = -1
	}
	
	fmt.Scan(&m)
	sc := bufio.NewScanner(os.Stdin)
	sc.Split(bufio.ScanWords)
	for i := 0; i < m; i++ {
		sc.Scan()
		s, _ := strconv.Atoi(sc.Text())
		sc.Scan()
		t, _ := strconv.Atoi(sc.Text())
		
		g[s] = append(g[s], t)
		g[t] = append(g[t], s)
	}
	for i := 0; i < n; i++ {
		if group[i] != -1 {
			continue
		}
		q := []int{i}
		for len(q) > 0 {
			pop := q[0]
			if len(q) > 1 {
				q = q[1:]
			} else {
				q = []int{}
			}
			if group[pop] == -1 {
				q = append(q, g[pop]...)
				group[pop] = i
			}
		}
	}
	sc.Scan()
	q, _ := strconv.Atoi(sc.Text())
	for i := 0; i < q; i++ {
		sc.Scan()
		s, _ := strconv.Atoi(sc.Text())
		sc.Scan()
		t, _ := strconv.Atoi(sc.Text())

		if group[s] == group[t] {
			fmt.Println("yes")
		} else {
			fmt.Println("no")
		}
	}
}

func root(i int, group *[]int) int {
	if i == (*group)[i] {
		return i
	}
	(*group)[i] = root((*group)[i], group)
	return (*group)[i]
}

C++: #include <bits/stdc++.h>

using namespace std;

#define rep(i, n) for(int i = 0; i < (int)n; ++i)
#define FOR(i, a, b) for(int i = a; i < (int)b; ++i)
#define rrep(i, n) for(int i = ((int)n - 1); i >= 0; --i)

typedef long long ll;
typedef long double ld;

const int Inf = 1e9;
const double EPS = 1e-9;
const int MOD = 1e9 + 7;

class UnionFind {
    public:
        vector<int> rank, p, size;

        UnionFind() {}
        UnionFind(int s) {
            rank.resize(s, 0);
            p.resize(s, 0);
            size.resize(s, 0);
            rep (i, s) init(i);
        }

        void init(int x) {
            p[x] = x;
            rank[x] = 0;
            size[x] = 1;
        }

        bool isSame(int x, int y) {
            return root(x) == root(y);
        }

        void unite(int x, int y) {
            if (isSame(x, y)) return;
            link(root(x), root(y));
        }

        void link(int x, int y) {
            if (rank[x] > rank[y]) {
                p[y] = x;
                size[x] += size[y];
            } else {
                p[x] = y;
                size[y] += size[x];
                if (rank[x] == rank[y]) {
                    rank[y]++;
                }
            }
        }

        int root(int x) {
            if (x != p[x]) {
                p[x] = root(p[x]);
            }
            return p[x];
        }

        int getSize(int x) {
            return size[root(x)];
        }
};

int main() {
    cin.tie(nullptr);
    ios::sync_with_stdio(0);
    int n, m, q;
    cin >> n >> m;
    UnionFind uf = UnionFind(n);
    rep (i, m) {
        int s, t;
        cin >> s >> t;
        uf.unite(s, t);
    }
    cin >> q;
    rep (i, q) {
        int s, t;
        cin >> s >> t;
        if (uf.isSame(s, t)) cout << "yes" << endl;
        else cout << "no" << endl;
    }
    
    return 0;
}

C++: #include <iostream>
#include <vector>
#include <stack>

using namespace std;
static const int MAX = 100000;
static const int NIL = -1;

int n;
vector<int> G[MAX];
int color[MAX];

void dfs(int r, int c) {
  stack<int> S;
  S.push(r);
  color[r] = c;
  while(!S.empty()) {
    int u = S.top();
    S.pop();
    for(int i = 0; i < G[u].size(); i++) {
      int v = G[u][i];
      if(color[v] == NIL) {
        color[v] = c;
        S.push(v);
      }
    }
  }
}

void assignColor() {
  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 main (void) {
  int s, t, m, q;

  cin >> n >> m;

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

  assignColor();

  cin >> q;

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

C++: #include <bits/stdc++.h>
using namespace std;

#define NIL -1

void dfs(int r, int id, vector<vector<int>> &G, vector<int> &color) {
    stack<int> S;
    S.push(r);

    color[r] = id;
    while (!S.empty()) {
        int u = S.top();
        S.pop();

        for (int i = 0; i < G[u].size(); i++) {
            int v = G[u][i];
            if (color[v] == NIL) {
                color[v] = id;
                S.push(v);
            }
        }
    }
}

void assignColor(vector<vector<int>> &G, vector<int> &color) {
    int id = 1;

    for (int i = 0; i < G.size(); i++)
        color[i] = NIL;

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

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

    vector<vector<int>> G(n);
    vector<int> color(n);

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

    // グループ分け
    assignColor(G, color);

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

C++: #include <bits/stdc++.h>
using namespace std;
typedef long long ll;
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }
const ll INF = 1LL << 60;
const ll MOD = 1000000007;

int N, M;
int cnt = 0;
vector<vector<int>> G;

vector<int> seen;
void dfs(int v) {
    seen[v] = cnt;

    for (auto nv : G[v]) {
        if (seen[nv] != -1) continue;

        dfs(nv);
    }
}

int main() {
    cin >> N >> M;
    G.resize(N);
    seen.assign(N, -1);
    for (int i = 0; i < M; i++) {
        int a, b; cin >> a >> b;
        G[a].push_back(b);
        G[b].push_back(a);
    }

    for (int v = 0; v < N; v++) {
        if (seen[v] != -1) continue;

        dfs(v);
        cnt++;
    }

    int q;  cin >> q;
    for (int i = 0; i < q; i++) {
        int a, b; cin >> a >> b;
        if (seen[a] == seen[b]) {
            cout << "yes" << endl;
        } else {
            cout << "no" << endl;
        }
    }
    return 0;
}

C++: #include <stdio.h>
#include <iostream>
#include <vector>
using namespace std;

#define MAX_N 100000
#define MAX_M 100000

vector<int> G[MAX_N];

int main(void){
    int n, m;
    scanf("%d %d\n", &n, &m);
    for(int i = 0; i < m; i++){
        int a, b;
        scanf("%d %d", &a, &b);
        G[a].push_back(b);
        G[b].push_back(a);
    }

    int q;
    scanf("%d", &q);
    for(int i = 0; i < q; i++){
        int a, b;
        scanf("%d %d", &a, &b);

        for(int j = 0; j < G[a].size(); j++){
            if(G[a][j] == b){
                printf("yes\n");
                break;
            }
            if(j == G[a].size() - 1){
                printf("no\n");
            }
        }
    }
}