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++: #include<bits/stdc++.h>
using namespace std;
int d[100001];
int main(void){
	int	n,m;
	int s,t;
	int q;
	int i,j;
	int x,y;
	int cnt;
	vector<int>v[100001];
	queue<int>que;
	cin>>n>>m;
	for(i=0;i<m;i++){
		cin>>s>>t;
		v[s].push_back(t);
		v[t].push_back(s);
	}
	for(i=0;i<n;i++)	d[i]=0;
	cnt=0;
	for(i=0;i<n;i++){
		if(d[i]==0){
			cnt++;
			d[i]=cnt;
			que.push(i);
			while(!que.empty()){
				x=que.front();
				que.pop();
				for(j=0;j<v[x].size();j++){
					y=v[x][j];
					if(d[y]==0){
						d[y]=cnt;
						que.push(y);
					}
				}
			}
		}
	}
	cin>>q;
	for(i=0;i<q;i++){
		cin>>s>>t;
		cout<<((d[s]==d[t])?"yes":"no")<<endl;
	}
	
	return 0;
}

C++: #include <stdio.h>
#include <iostream>
#include <vector>
#include <queue>
using namespace std;

#define MAX_N 100000
#define MAX_M 100000
#define WHITE 1
#define GREY 2
#define BLACK 3

vector<int> G[MAX_N];
int V[MAX_N];
int V_num[MAX_N];

void init(void){
    for(int i = 0; i < MAX_N; i++){
        V[i] = WHITE;
        V_num[i] = i;
    }
}

void labeling(int target){
    queue<int> Q;
    Q.push(target);
    while(!Q.empty()){
        int num = Q.front(); Q.pop();
        for(int i = 0; i < G[num].size(); i++){
            if(V[G[num][i]] == WHITE){
                Q.push(G[num][i]);
                V[G[num][i]] = GREY;
                V_num[G[num][i]] = target;
            }
        }
        V[num] = BLACK;
    }
}

int main(void){
    init();
    int n, m;
    scanf("%d %d\n", &n, &m);
    for(int i = 0; i < m; i++){
        int a, b;
        scanf("%d %d", &a, &b);
        G[a].push_back(b);
        G[b].push_back(a);
    }

    for(int i = 0; i < n; i++){
        if(V[i] != WHITE){
            continue;
        }
        labeling(i);
    }

    int q;
    scanf("%d", &q);
    for(int i = 0; i < q; i++){
        int a, b;
        scanf("%d %d", &a, &b);
        if(V_num[a] == V_num[b]){
            printf("yes\n");
        }else{
            printf("no\n");
        }
    }

    /*
    for(int i = 0; i < n; i++){
        printf("%d %d\n", i, V_num[i]);
    }
    */
}

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> &arrived, int x, int y)
{
    if (arrived[y] != 0) return;
    queue<int> mq;
    mq.push(x);
    while(!mq.empty()) {
        int curr = mq.front();
        mq.pop();
        arrived[curr] = 2;
        for (int i = 0; i < sns[curr].size(); i++) {
            int next = sns[curr][i];
            if (arrived[next] == 0) {
                mq.push(next);
                arrived[next] = 1;
            }
        }
    }
}

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;
        bfs(sns, arrived, x, y);
        if (arrived[y]) cout << "yes" << endl;
        else cout << "no" << endl;
    }
    return 0;
}

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


#include<queue>
using namespace std;
int main()
{
    int person_number,relation_number;

    cin>>person_number>>relation_number;

    vector<vector<int > > list(person_number);
    for(int i=0;i<relation_number;i++)
    {
        int start,end;
        cin>>start>>end;
        int flag=0;
        for(auto n:list[start])
        {
            if(n==end)
                flag=1;
        }
        if(flag==0) 
        {
            list[start].push_back(end);
            list[end].push_back(start);
        }
    }

    int test_number;
    cin>>test_number;
for(int i=0;i<test_number;i++)
{
    int from,to;
    cin>>from>>to;
    queue<int> q;
    q.push(from);
    vector<int> ban_list;
    for(int i=0;i<person_number;i++)
    {
        ban_list.push_back(0);
    }
    ban_list[from]=1;
    for(;!q.empty();q.pop())
    {
        int flag=0;
        for(auto n:list[q.front()])
        {
            if(n==to) 
            { 
                flag=1;
                break;
            }
            if(ban_list[n]==0)
            {
                ban_list[n]=1;
                q.push(n);
            }
        }
        if(flag==1) break;
    }
    if(!q.empty()) cout<<"yes"<<endl;
    else cout<<"no"<<endl;
}
    return 0;
}