Go: package main

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

var (
	n     int
	G     [100000][]int
	color [100000]*int
)

func dfs(r int, c int) {
	S := Stack{}
	S.Push(r)
	color[r] = &c
	for !S.IsEmpty() {
		u := S.Pop()
		for i := 0; i < len(G[u]); i++ {
			v := G[u][i]
			if color[v] == nil {
				color[v] = &c
				S.Push(v)
			}
		}
	}
}

func assignColor() {
	id := 1
	for i := 0; i < n; i++ {
		color[i] = nil
	}
	for u := 0; u < n; u++ {
		if color[u] == nil {
			id++
			dfs(u, id)
		}
	}
}

func main() {
	sc := bufio.NewScanner(os.Stdin)
	sc.Split(bufio.ScanWords)
	sc.Scan()
	n, _ = strconv.Atoi(sc.Text())
	sc.Scan()
	r, _ := strconv.Atoi(sc.Text())

	for i := 0; i < r; 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)
	}
	assignColor()
	sc.Scan()
	qNum, _ := strconv.Atoi(sc.Text())
	for i := 0; i < qNum; i++ {
		sc.Scan()
		s, _ := strconv.Atoi(sc.Text())
		sc.Scan()
		t, _ := strconv.Atoi(sc.Text())
		if color[s] == color[t] {
			fmt.Println("yes")
		} else {
			fmt.Println("no")
		}
	}
}

// Stack is Stack
type Stack struct {
	stack []int
}

// Push new value
func (stack *Stack) Push(val int) {
	stack.stack = append(stack.stack, val)
}

// Pop new value
func (stack *Stack) Pop() int {
	val := stack.stack[len(stack.stack)-1]
	stack.stack = stack.stack[0 : len(stack.stack)-1]
	return val
}

// IsEmpty return true when stack is empty
func (stack *Stack) IsEmpty() bool {
	return len(stack.stack) == 0
}

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;
}

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

using namespace std;

static const int MAX = 100000;
static const int NIL = -1;

int n; //number of users
vector<int> G[MAX];
int color[MAX];

void dfs(int userid, int groupid) {
    stack<int> S;
    S.push(userid);
    color[userid] = groupid;
    while ( !S.empty() ) {
        int user = S.top(); S.pop();
        for (unsigned long i = 0; i < G[user].size(); i++) {
            int partner = G[user][i];
            //if partner is not member of a group -> join to user's group
            if (color[partner] == NIL) {
                color[partner] = groupid;
                //add partner to stack, then check partner's partner list (use while)
                S.push(partner);
            }
        }
    }
}

//create a group list named as color
//result is color = [1, 1, 1, 2, 2, 3, 3, 3, 3, 3]
void assingColor() {
    int id = 1;
    for (int i = 0; i < n; i++) color[i] = NIL; // create empty group list
    for (int u = 0; u < n; u++) {
        //u = user id, id = group id
        if (color[u] == NIL) dfs(u, id++); //fill group list with dfs
    }
    //for (int i = 0; i < n; i++) cout << color[i] << " ";
    //cout << endl;
}

int main()
{
    int m; //number of relationships
    int s, t; //user and partner id
    int q; //number of question
    cin >> n >> m;
    for (int i = 0; i < m; i++) {
        cin >> s >> t;
        G[s].push_back(t); //push user's partner id to user relationship list
        G[t].push_back(s); //push user id to user's partner relationship list
    }
    assingColor();

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