Go: package main

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

// Node 頂点
type Node struct {
	gid  int   // グループID
	edge []int // 隣接辺
}

// NoID グループIDなし
const NoID = -1

// NewNode 頂点の生成
func NewNode() *Node {
	return &Node{gid: NoID, edge: []int{}}
}

func parseNode(nodes []*Node, gid int, queue []int) {
	if len(queue) == 0 {
		return
	}
	var nextQ []int
	for _, id := range queue {
		node := nodes[id]
		if node.gid == NoID {
			node.gid = gid
			for _, edge := range node.edge {
				nextQ = append(nextQ, edge)
			}
		}
	}
	parseNode(nodes, gid, nextQ)
	return
}
func digNode(nodes []*Node, id, gid int) {
	node := nodes[id]
	if node.gid != NoID {
		// 探索済み
		return
	}
	node.gid = gid
	for _, edge := range node.edge {
		digNode(nodes, edge, gid)
	}
	return
}

func main() {
	scanner := bufio.NewScanner(os.Stdin)
	n, m := eGetInt2(scanner)

	nodes := make([]*Node, n)
	for i := 0; i < n; i++ {
		nodes[i] = NewNode()
	}

	for i := 0; i < m; i++ {
		a, b := eGetInt2(scanner)
		nodes[a].edge = append(nodes[a].edge, b)
		nodes[b].edge = append(nodes[b].edge, a)
	}

	for i := 0; i < n; i++ {
		// 幅優先探索
		// gid := i
		// queue := []int{i}
		// parseNode(nodes, gid, queue)

		// 深さ優先探索
		digNode(nodes, i, i)
	}

	q := eGetInt(scanner)
	for i := 0; i < q; i++ {
		a, b := eGetInt2(scanner)
		if nodes[a].gid == nodes[b].gid {
			fmt.Println("yes")
		} else {
			fmt.Println("no")
		}
	}
}

func eGetInt(scanner *bufio.Scanner) int {
	t := eAtoi(strings.Fields(eGetline(scanner)))
	return t[0]
}
func eGetInt2(scanner *bufio.Scanner) (int, int) {
	t := eAtoi(strings.Fields(eGetline(scanner)))
	return t[0], t[1]
}

func eGetline(p *bufio.Scanner) string {
	if !p.Scan() {
		if err := p.Err(); err != nil {
			log.Fatal(err.Error())
		}
		return ""
	}
	return p.Text()
}

func eAtoi(s []string) []int {
	ints := make([]int, len(s))
	var err error
	for i, e := range s {
		ints[i], err = strconv.Atoi(e)
		if err != nil {
			log.Fatal(err.Error())
		}
	}
	return ints
}

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

#define inf 1000000007

using namespace std;

vector<vector<int> > connect;
vector<int> visited;
int n;

void dfs(int start,int c){
	stack<int> st;
	st.push(start);
	while(!st.empty()){
		int k = st.top();
		visited[k] = c;
		st.pop();
		for(int i=0;i<connect[k].size();++i){
			int tmp = connect[k][i];
			if(visited[tmp]==-1){
				st.push(tmp);
			}
		}
	}
}

int main(){
	int m,q;
	cin >> n >> m;
	connect.resize(n);
	visited.resize(n);
	for(int i=0;i<m;++i){
		int s,t;
		cin >> s >> t;
		connect[s].push_back(t);
		connect[t].push_back(s);
	}
	int c = 0;
	for(int i=0;i<n;++i)visited[i] = -1;
	for(int i=0;i<n;++i){
		if(visited[i] == -1){
			dfs(i,c);
			c++;
		}
	}
	cin >> q;
	vector<bool> res(q);
	for(int i=0;i<q;++i){
		int from,to;
		cin >> from >> to;
		if(visited[from] == visited[to]){
			res[i] = true;
		}else{
			res[i] = false;
		}
	}
	for(int i=0;i<q;++i){
		if(res[i])cout << "yes" << "\n";
		else cout << "no" << "\n";
	}
}

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

void bfs(int s);

int n_user,m,*deg;
vector<int> *G; 

int main(void){
	cin>>n_user>>m;
	deg = new int[n_user];
	G = new vector<int>[n_user];
	for(int i=0;i<n_user;i++)
		deg[i] = -1;

	int user1,user2;
	for(int i=0;i<m;i++){
		cin>>user1>>user2;
		G[user1].push_back(user2);
		G[user2].push_back(user1);
	}

	for(int i=0;i<n_user;i++){
		cout<<i<<" : ";
		for(int j=0;j<G[i].size();j++){
			cout<<G[i][j]<<" ";
		}
		cout<<endl;
	}

	for(int i=0;i<n_user;i++) bfs(i);

	int question,s,t;
	cin>>question;
	for(int i=0;i<question;i++){
		cin>>s>>t;
		if(deg[s]!=-1){
			if(deg[s]==deg[t])
				cout<<"yes"<<endl;
			else
				cout<<"no"<<endl;
		}
	}

	delete [] G; delete [] deg;
}

void bfs(int s){
	queue<int> q;
	q.push(s);
	if(deg[s]==-1) deg[s] = s;
	else return ;

	int u;
	while(!q.empty()){
		u = q.front();
		q.pop();
		for(int v=0;v<G[u].size();v++){
			if(deg[G[u][v]]==-1){
				deg[G[u][v]] = deg[u];
				q.push(G[u][v]);
			}
		}
	}
}

C++: #include <iostream>
#include <algorithm>
#include <climits>
#include <vector>
#include <stack>
#include <queue>
#include <set>
#include <map>
using namespace std;
vector<int> g[100000];
vector<int> c(100000);

void dfs(int v, int col) {
    c[v] = col;
    for (int i = 0; i < g[v].size(); ++i) {
        if(c[g[v][i]] == 0) dfs(g[v][i], col);
    }
}

int main() {
    int n, m, q;
    cin >> n>> m;
    for (int i = 0; i < m; ++i) {
        int v, w;
        cin >> v >> w;
        g[w].push_back(v);
        g[v].push_back(w);
    }

    for (int k = 0; k < n; ++k) {
        c[k] = 0;
    }

    int col = 1;
    for (int j = 0; j < n; ++j) {
        if(!c[j]) {
            dfs(j, col);
            col++;
        }
    }

    cin >> q;
    for (int l = 0; l < q; ++l) {
        int v,w;
        cin >> v >> w;
        if(c[v] == c[w]) cout << "yes";
        else cout << "no";
        cout << endl;

    }


    return 0;
}

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

#define rep(i, n) for (int i = 0; i < (int)(n); ++i)

const int SIZE = 100001;
int group[SIZE];

void assignGroup(int u, int g, std::vector<int> *a) {
  if (group[u] != 0) return;

  group[u] = g;
  // for (int i = 0; i < a[u].size(); ++i) {
  //   if (a[u][i] && group[i] == 0) assignGroup(i, g, a);
  // }
  for (auto v : a[u]) {
    // printf("u: %d, v: %d, group[u]: %d, group[v]: %d\n", u, v, group[u],
    //        group[v]);
    if (group[v] == 0) assignGroup(v, g, a);
  }
}

bool isConnected(int s, int t) { return group[s] == group[t]; }

int main() {
  int n, m;
  std::cin >> n >> m;
  std::vector<int> a[n];

  rep(i, m) {
    int s, t;
    std::cin >> s >> t;
    a[s].push_back(t);
    a[t].push_back(s);
  }

  // std::cout << "/* message */" << '\n';
  // rep(i, n) {
  //   for (auto v : a[i]) std::cout << v << ' ';
  //   std::cout << '\n';
  // }
  // std::cout << "/* message */" << '\n';

  int g = 0;
  rep(i, n) {
    if (group[i] == 0) { assignGroup(i, ++g, a); }
  }

  // rep(i, n) std::cout << group[i] << ' ';

  int q;
  std::cin >> q;
  rep(i, q) {
    int s, t;
    std::cin >> s >> t;
    if (isConnected(s, t))
      std::cout << "yes" << '\n';
    else
      std::cout << "no" << '\n';
  }

  return 0;
}

C++: //
// Created by ?????°?????? on 2016/05/15.
//

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

const int MAX = (1 << 21);
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(){
    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;
}