Go: package main

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

const MAX = 100000

type Queue struct {
	head      int
	tail      int
	container [MAX]int
}

func (q *Queue) push(n int) {
	q.container[q.tail] = n
	q.tail = (q.tail + 1) % MAX
}

func (q *Queue) pop() int {
	res := q.container[q.head]
	q.head = (q.head + 1) % MAX
	return res
}

func (q *Queue) isEmpty() bool {
	return q.head == q.tail
}

var sc = bufio.NewScanner(os.Stdin)
var route [][]int
var SEEN [MAX]bool
var GROUP [MAX]int

func scanInt() int {
	num, _ := strconv.Atoi(scanString())
	return num
}

func scanString() string {
	sc.Scan()
	return sc.Text()
}

func init() {
	sc.Split(bufio.ScanWords)
}

func bfs(start, group int) {
	que := Queue{}
	que.push(start)

	for !que.isEmpty() {
		id := que.pop()

		if SEEN[id] {
			continue
		}
		SEEN[id] = true
		GROUP[id] = group

		for _, next := range route[id] {
			que.push(next)
		}
	}
}

func main() {
	n, m := scanInt(), scanInt()
	route = make([][]int, n)
	for i := 0; i < m; i++ {
		s, t := scanInt(), scanInt()
		route[s] = append(route[s], t)
		route[t] = append(route[t], s)
	}

	for i := 0; i < n; i++ {
		if !SEEN[i] {
			bfs(i, i+1)
		}
	}

	w := bufio.NewWriter(os.Stdout)
	q := scanInt()
	for i := 0; i < q; i++ {
		s, t := scanInt(), scanInt()
		if GROUP[s] == GROUP[t] {
			fmt.Fprintln(w, "yes")
		} else {
			fmt.Fprintln(w, "no")
		}
	}
	w.Flush()
}

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

using namespace std;

struct UnionFind {
  vector<int> data;
  UnionFind(int size) : data(size, -1) { }
  bool unionSet(int x, int y) {
    x = root(x); y = root(y);
    if (x != y) {
      if (data[y] < data[x]) swap(x, y);
      data[x] += data[y]; data[y] = x;
    }
    return x != y;
  }
  bool findSet(int x, int y) {
    return root(x) == root(y);
  }
  int root(int x) {
    return data[x] < 0 ? x : data[x] = root(data[x]);
  }
  int size(int x) {
    return -data[root(x)];
  }
};

int main() {
  int n, m, q;
  cin >> n >> m;
  UnionFind uf(n);
  for (int i = 0; i < m; ++i) {
    int s, t;
    cin >> s >> t;
    uf.unionSet(s, t);
  }
  cin >> q;
  for (int i = 0; i < q; ++i) {
    int s, t;
    cin >> s >> t;
    if (uf.findSet(s, t)) {
      cout << "yes" << endl;
    } else {
      cout << "no" << endl;
    }
  }
  return 0;
}

C++: // ALDS1_11_D.cpp
// Graph I - Connected Components

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

void bfs(vector<vector<int>> &sns, vector<int> &color, int x)
{
    if (color[x] != -1 || sns[x].empty()) return;
    queue<int> mq;
    mq.push(x);
    while(!mq.empty()) {
        int curr = mq.front();
        mq.pop();
        color[curr] = x;
        for (int i = 0; i < sns[curr].size(); i++) {
            int next = sns[curr][i];
            if (color[next] == -1) {
                mq.push(next);
                color[next] = x;
            }
        }
    }
}

void assignColor(vector<vector<int>> &sns, vector<int> &color)
{
    for (int i = 0; i < sns.size(); i++) {
        bfs(sns, color, i);
    }
}

int main()
{
//    freopen("ALDS1_11_D_in22.txt", "r", stdin);
//    freopen("out22.txt", "w", stdout);
    int m, n, q;
    cin >> n >> m;
    vector<vector<int> > sns(n, vector<int>());
    int x, y;
    for (int i = 0; i < m; i++) {
        cin >> x >> y;
        sns[x].push_back(y);
        sns[y].push_back(x);
    }
    vector<int> color(n, -1);
    assignColor(sns, color);
    cin >> q;
    while (q--) {
        cin >> x >> y;
        if (color[x] == color[y] && color[x] != -1) cout << "yes" << endl;
        else cout << "no" << endl;
    }
    return 0;
}