Go: package main

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

var scanner = bufio.NewScanner(os.Stdin)

func nextString() string {
	scanner.Scan()
	return scanner.Text()
}

func nextInt() int {
	n, err := strconv.Atoi(nextString())
	if err != nil {
		fmt.Printf("strconv.Atoi failed: %v\n", err)
	}
	return n
}

func newGraph(nNodes int) *Graph {
	g := Graph{}
	g.nodes = make([]*GraphNode, nNodes)
	for iNode := 0; iNode < len(g.nodes); iNode++ {
		g.nodes[iNode] = &GraphNode{}
		g.nodes[iNode].key = GraphNodeKey(iNode)
	}
	return &g
}

var infty = 1000000000

type GraphNodeKey int

// GraphNode is a node for undirected graph
type GraphNode struct {
	key       GraphNodeKey
	adjacents []*GraphNode
	visited   bool
	d, f      int
	parent    *GraphNode
	cc        int
}

func (g *Graph) setAdjacent(l, r GraphNodeKey) {
	g.nodes[l].adjacents = append(g.nodes[l].adjacents, g.nodes[r])
}

// Graph is a undirected graph
type Graph struct {
	nodes []*GraphNode
}

func (g *Graph) initialize() {
	for iNode := 0; iNode < len(g.nodes); iNode++ {
		g.nodes[iNode].visited = false
		g.nodes[iNode].d = infty
		g.nodes[iNode].f = infty
		g.nodes[iNode].parent = nil
		g.nodes[iNode].cc = -1 // 22.3-12
	}
}

type QueueEntry struct {
	node *GraphNode
	next *QueueEntry
}

type Queue struct {
	head, tail *QueueEntry
}

func (q *Queue) enqueue(node *GraphNode) {
	entry := QueueEntry{}
	entry.node = node

	if q.tail == nil {
		q.head = &entry
		q.tail = &entry
		return
	}

	q.tail.next = &entry
	q.tail = q.tail.next
}

func (q *Queue) dequeue() *QueueEntry {
	if q.head == nil {
		return nil
	}
	poped := q.head
	q.head = q.head.next
	if q.head == nil {
		q.tail = nil
	}
	return poped
}

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

var time = 0

func fillDistancesByDepthFirstSearch(g *Graph) {
	g.initialize()
	time = 0
	cc := 0

	for _, u := range g.nodes {
		if !u.visited {
			dfsVisit(g, u, cc)
			cc++
		}
	}
}

func dfsVisit(g *Graph, u *GraphNode, cc int) {
	time++
	u.d = time
	u.cc = cc

	u.visited = true
	for _, v := range u.adjacents {
		if !v.visited {
			v.parent = u
			dfsVisit(g, v, cc)
		}
	}
	time++
	u.f = time
}

func main() {
	scanner.Split(bufio.ScanWords)

	nUsers := nextInt()
	nEdges := nextInt()
	graph := newGraph(nUsers)
	for iEdge := 0; iEdge < nEdges; iEdge++ {
		l := GraphNodeKey(nextInt())
		r := GraphNodeKey(nextInt())
		graph.setAdjacent(l, r)
		graph.setAdjacent(r, l)
	}

	fillDistancesByDepthFirstSearch(graph)

	nQueries := nextInt()
	for iQuery := 0; iQuery < nQueries; iQuery++ {
		l := GraphNodeKey(nextInt())
		r := GraphNodeKey(nextInt())

		// fmt.Println(graph.nodes[l].d, graph.nodes[r].d, graph.nodes[r].f, graph.nodes[l].f)
		if graph.nodes[l].cc == graph.nodes[r].cc {
			fmt.Println("yes")
		} else {
			fmt.Println("no")
		}
	}
}

C++: //ALDS1_11D
#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(){
 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++: // ALDS1_11_D.cpp
// Graph I - Connected Components

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

void dfs(vector<vector<int>> &sns, vector<int> &arrived, int x, int y)
{
    if (arrived[y] != 0 && arrived[x] == 2) return;
    arrived[x]++;
    for (int i = 0; i < sns[x].size(); i++) {
        int next = sns[x][i];
        if (arrived[next] == 0) {
            dfs(sns, arrived, next, y);
        }
    }
    arrived[x]++;
}

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);
    }

    cin >> q;
    while (q--) {
        vector<int> arrived(n);
        cin >> x >> y;
        dfs(sns, arrived, x, y);
        if (arrived[y]) cout << "yes" << endl;
        else cout << "no" << endl;
    }
    return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef vector<int> vi;
typedef vector<vector<int>> vvi;

void dfs(const vvi &to, vi &id, int u, int val) {
    id[u] = val;
    for (int v: to[u]) {
        if (id[v] < 0) dfs(to, id, v, val);
    }
};

int main() {
    int n, m, s, t, q, u, v;
    cin >> n >> m;
    vvi to(n);
    for (int i=0; i<m; ++i) {
        cin >> s >> t;
        to[s].push_back(t);
        to[t].push_back(s);
    }
    vi id(n, -1);
    for (int i=0; i<n; ++i) {
        if (id[i] < 0) dfs(to, id, i, i);
    }
    cin >> q;
    for (int i=0; i<q; ++i) {
        cin >> u >> v;
        cout << (id[u] == id[v] ? "yes" : "no") << endl;
    }
    return 0;
}

C++: #include <stdio.h>

#define MAX_USER (100000)

/*

1)initial state

	0    1    2    3    4    5...

2)create friendship 
	friend: 0 and 1
	friend: 2 and 3

	0    2    4
    |    |
	1    3

3)and more
	friend: 2 and 4

	0       2      5
	|      / \
	1     3---4

*/



struct UserInfo
{
	long uid;
	UserInfo* next;
	UserInfo* prev;
};

int examine_friendship( const UserInfo* user_info , long uid1 , long uid2 )
{
	UserInfo* uid_ptr = user_info[ uid1 ].next;

	while( uid_ptr->uid != uid1 )
	{
		if( uid_ptr->uid == uid2 )
		{
			return 1;
		}
		uid_ptr = uid_ptr->next;
	}
	return 0;
}

int main( int argc , char** argv )
{
	//read setting
	long user_count;
	long friendship_count;
	scanf( "%ld %ld" , &user_count , &friendship_count );

	//initialize
	UserInfo*  user_info = new UserInfo[ user_count ];
	for( long i = 0 ; i < user_count ; i++ )
	{
		user_info[ i ].uid = i;
		user_info[ i ].next = &user_info[ i ];
		user_info[ i ].prev = &user_info[ i ];
	}

	//read user friendship
	for( long i = 0 ; i < friendship_count ; i++ )
	{
		long uid1;
		long uid2;
		scanf( "%ld %ld" , &uid1 , &uid2 );

		//update internal data
		UserInfo* uid1_ptr = &user_info[ uid1 ];
		UserInfo* uid2_ptr = &user_info[ uid2 ];
		UserInfo* uid1_next_ptr = uid1_ptr->next;

		uid1_ptr->next = uid2_ptr;
		uid2_ptr->prev = uid1_ptr;

		uid1_next_ptr->prev = uid2_ptr;
		uid2_ptr->next = uid1_next_ptr;
	}

	//read number of question
	long question_count;
	scanf( "%ld" , &question_count );

	//process question
	for( long i = 0 ; i < question_count ; i++ )
	{
		long uid1;
		long uid2;
		scanf( "%ld %ld" , &uid1 , &uid2 );

		if( examine_friendship( user_info , uid1 ,uid2 ) )
		{
			printf( "yes\n" );
		}
		else
		{
			printf( "no\n" );
		}
	}

	return 0;
}

C++: #include<iostream>
#define MAX 100
using namespace std;

int main() {
	int i, n, m, q, a, b, gnum = 0, ptog[MAX] = {};

	cin >> n >> m;
	for (i = 0; i < m; i++) {
		cin >> a >> b;
		if (ptog[a] != 0)ptog[b] = ptog[a];
		else if (ptog[b] != 0)ptog[a] = ptog[b];
		else ptog[a] = ptog[b] = ++gnum;
	}

	cin >> q;
	for (i = 0; i < q; i++) {
		cin >> a >> b;
		if (ptog[a] == ptog[b])cout << "yes\n";
		else cout << "no\n";
	}
}