Go: package main

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

func main() {
	var n,m int
	fmt.Scan(&n)
	group := make([]int, n)
	for i := 0; i < n; i++ {
		group[i] = i
	}
	
	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())

		if group[s] < group[t] {
			group[t] = group[s]
		} else {
			group[s] = group[t]
		}
	}

	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 root(s, &group) == root(t, &group) {
			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>
#define rep(i, a, b) for(int i = a; i < b; i++)
#define Rep(i, a, b) for(int i = a; i <= b; i++)
#define _GLIBCXX_DEBUG
#define Vl vector<ll>
#define Vs vector<string>
#define Vp vector<pair<ll, ll>>
#define ll long long
#define ALL(v) (v).begin(),(v).end()
using namespace std;
const double pi = acos(-1.0);
const ll MOD = 1e9 + 7;
const ll INF = 1LL << 60;
using Graph = vector<vector<ll>>;

ll n;
vector<ll> fri[100100];
int color[100100];

void dfs(int r, int c){
  stack<ll> s;
  s.push(r);
  color[r] = c;
  while(!s.empty()){
    int u = s.top(); s.pop();
    rep(i, 0, fri[u].size()){
      int v = fri[u][i];
      if(color[v] == -1){
        color[v] = c;
        s.push(v);
      }
    }
  }
}

void assignColor(){
  int id = 1;
  rep(i, 0, n) color[i] = -1;
  rep(u, 0, n){
    if(color[u] == -1) dfs(u, id++);
  }
}

int main() {
  ll m; cin >> n >> m;
  
  rep(i, 0, m){
    ll a, b; cin >> a >> b;
    fri[a].push_back(b);
    fri[b].push_back(a);
  }

  assignColor();

  ll q; cin >> q;
  rep(i, 0, q){
    ll a, b; cin >> a >> b;
    if(color[a] == color[b]) puts("yes");
    else puts("no");
  }

  return 0;
}

C++: #include<iostream>
#include<vector>
#include<cstring>
#include<algorithm>
#include<queue>
#define P pair<int, int>

using namespace std;

int main(){
  int n, m, q, c[100009];
  vector<int> G[100009];
  queue<int> Q;
  memset(c, -1, sizeof(c));
  cin >> n >> m;
  for(int i=0;i<m;i++){
    int s, e;
    cin >> s >> e;
    G[s].push_back(e);
    G[e].push_back(s);
  }
  for(int i=0;i<n;i++){
    if(c[i]!=-1)continue;
    c[i] = i;
    Q.push(i);
    while(!Q.empty()){
      int node = Q.front();Q.pop();
      for(int j=0;j<G[node].size();j++){
        if(c[G[node][j]]==-1){
          c[G[node][j]] = i;
          Q.push(G[node][j]);
        }
      }
    }
  }
  cin >> q;
  for(int i=0;i<q;i++){
    int s, e;cin >> s >> e;
    cout << (c[s] == c[e]? "yes": "no") << endl;
  }
}

C++: // -*- mode:c++; coding:utf-8; c-basic-offset:2; -*-
// ALDS1_11_D: Connected Components

#include <algorithm>
#include <climits>
#include <cstdio>
#include <vector>

using uint = unsigned int;

class Graph {
  std::vector<std::vector<uint>> g_;
  std::vector<uint> root_;
  
public:
  Graph(uint n)
  {
    g_.resize(n);
    root_.resize(n);
  }

  void add(uint from, uint to)
  {
    g_[from].push_back(to);
  }

  void setup()
  {
    std::fill(root_.begin(), root_.end(), UINT_MAX);
    for (auto i = 0u; i < g_.size(); ++i ) {
      dfs(i, i);
    }
  }

  bool reachable(uint from, uint to) const
  {
    return root_[from] == root_[to];
  }

private:
  void dfs(uint i, uint root)
  {
    if (root_[i] != UINT_MAX) return;
    root_[i] = root;
    for (auto j = 0u; j < g_[i].size(); ++j) {
      dfs(g_[i][j], root);
    }
  }
  
};

int main()
{
  uint n, m;
  std::scanf("%u %u", &n, &m);

  Graph g(n);

  uint s, t;
  for (auto i = 0u; i < m; ++i) {
    std::scanf("%u %u", &s, &t);
    g.add(s, t);
  }
  g.setup();

  uint q;
  std::scanf("%u", &q);
  for (auto i = 0u; i < q; ++i) {
    std::scanf("%u %u", &s, &t);
    std::puts(g.reachable(s, t) ? "yes" : "no");
  }
}

// eof

C++: #include <bits/stdc++.h>
using namespace std;
#define REP(i, s, n) for (int i = s; i < n; ++i)
#define rep(i, n) REP(i, 0, n)
#define SORT(c) sort((c).begin(), (c).end())
#define IINF INT_MAX
#define LLINF LLONG_MAX
#define DEBUG true
// sort(a.begin(), a.end(), std::greater<int>());

/*
std::vector<std::string> split(const std::string &input, char delimiter)
{
    std::istringstream stream(input);

    std::string field;
    std::vector<std::string> result;
    while (std::getline(stream, field, delimiter))
    {
        result.push_back(field);
    }
    return result;
}
*/
pair<int, int> data[100000];
bool finds[100000];
int n, m;
/*
int dfs(int foo, int timer)
{
    //foo is node number
    if (finds[foo].first != -1)
        return timer;
    finds[foo].first = ++timer;
    int result = timer;
    if (data[foo].size() != 0)
    {
        rep(i, data[foo].size())
        {
            result = dfs(data[foo][i], result);
        }
    }
    finds[foo].second = ++result;
    return result;
}
*/

bool dfs(int foo, int goal)
{
    bool ans = false;
    rep(i, m)
    {
        if (data[i].first == foo && data[i].second == goal)
            return true;
        if (data[i].first == foo)
        {
            if (finds[i] == true)
                continue;
            finds[i] = true;
            ans = dfs(data[i].second, goal);
        }
    }
    return ans;
}
int main()
{
    cin >> n >> m;
    rep(i, m)
    {
        cin >> data[i].first >> data[i].second;
    }
    int q;
    cin >> q;
    rep(i, q)
    {
        int left, right;
        cin >> left >> right;
        if (dfs(left, right) || dfs(right, left))
            cout << "yes";
        else
            cout << "no";
        cout << endl;
        rep(j, m) finds[j] = false;
    }
    return 0;
}

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

typedef uint32_t u32;

template<u32 N_>
class UnionFindTree {
private:
  u32 par[N_];
  u32 rank[N_];
public:
  UnionFindTree(u32 n) {
    assert(n < N_);
    for(u32 i = 0; i < n; ++i) {
      par[i] = i;
      rank[i] = 0;
    }
    return;
  }
  int find(u32 x) {
    if( par[x] == x ) return x;
    return par[x] = find(par[x]);
  }
  void unite(u32 x, u32 y) {
    x = find(x);
    y = find(y);
    if( x == y ) return;
    if( rank[x] < rank[y] ) {
      par[x] = y;
      return;
    }
    par[y] = x;
    if( rank[x] == rank[y] ) rank[x] += 1;
    return;
  }  
};

int main() {

  u32 n, m;
  std::cin >> n >> m;

  UnionFindTree<200000> uft(m);

  for(u32 i = 0; i < m; ++i) {
    u32 x, y;
    std::cin >> x >> y;
    uft.unite(x, y);
  }

  u32 q;
  std::cin >> q;

  for(u32 i = 0; i < q; ++i) {
    u32 x, y;
    std::cin >> x >> y;
    std::cout << (uft.find(x) == uft.find(y) ? "yes" : "no") << std::endl;
  }
  
  return 0;
}

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

void set_color(const vector<vector<int> >& u, int p, vector<int>& color, int c) {
    if (color[p] != -1) return;
    color[p] = c;
    for (int i = 0; i < u[p].size(); i++) {
        set_color(u, u[p][i], color, c);
    }
}

bool is_friend(const vector<vector<int> >& u, int s, int t){
    vector<int> color(u.size(), -1);
    int c = 0;
    set_color(u, s, color, c++);
    return color[s] == color[t];
}
int main(){
    int n, m;
    cin >> n >> m;
    vector<vector<int> > u(n);
    for (int i = 0; i < m; i++) {
        int s, t;
        cin >> s >> t;
        u[s].push_back(t);
        u[t].push_back(s);
    }
    int q;
    cin >> q;
    for (int i = 0; i < q; i++) {
        int s, t;
        cin >> s >> t;
        if (is_friend(u, s, t)) {
            cout << "yes" << endl;
        } else {
            cout << "no"  << endl;
        }
    }
    return 0;
}