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<iostream>
#include<map>
#include<set>

using namespace std;

int main(){
	int n, m, s, t, q, i, j;
	int id, stc = 0;
	bool answer_yes = false;
	map<int, set<int> > Adj;
	map<int, int> Stack;
	set<int> Check;
	set<int>::iterator it, itend;

	cin >> n >> m;
	for (i = 0; i < m; i++) {
		cin >> s >> t;
		Adj[s].insert(t);
		Adj[t].insert(s);
	}

	/*for (auto it1 = Adj.begin(); it1 != Adj.end(); it1++) {
		cout << "\n" << it1->first << " : " << flush;
		for (auto it2 = it1->second.begin(); it2 != it1->second.end(); it2++) {
			cout << *it2 << " " << flush;
		}
	}
	cout << endl;*/

	cin >> q;
	for (i = 0; i < q; i++) {
		cin >> s >> t;
		
		// calculate
		Stack.insert(pair<int, int>(stc, s));
		Check.insert(s);
		while (!Stack.empty()) {
			id = Stack[stc];
			//cout << "\nid : " << id << " stc : " << stc << endl;
			itend = Adj[id].end();
			for (it = Adj[id].begin(); it != itend; it++) {
				//cout << *it << " " << flush;
				if (Check.find(*it) == Check.end()) {
					if (*it == t) {
						answer_yes = true;
						Stack.clear();
						break;
					}
					stc++;
					Stack.insert(pair<int, int>(stc, *it));
					Check.insert(*it);
					break;
				}
			}
			if (it == itend) {
				Stack.erase(stc);
				stc--;
			}
		}
		if (answer_yes) {
			cout << "yes" << endl;
		} else {
			cout << "no" << endl;
			Stack.clear();
		}
		answer_yes = false;
		Check.clear();
		stc = 0;
	}
	
	return 0;
}

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

#define REP(i, n) for(int i=0;i<(int)(n);i++)
#define ALL(x) (x).begin(),(x).end()
const int INF = 1e9;

using namespace std;
int n, m;
struct node {
    int parent;
};

int main() {
    cin >> n >> m;
    node person[n];
    REP(i, n)
        person[i].parent = -1;
    REP(i, m){
        int s, t;
        cin >> s >> t;
        if(person[s].parent == -1){
            person[s].parent = s;
            person[t].parent = s;
        }
        else
            person[t].parent = person[s].parent;
    }
    int q;
    cin >> q;
    REP(i, q){
        int s, t;
        cin >> s >> t;
        if(person[s].parent != -1 && person[t].parent != -1  && person[s].parent == person[t].parent)
            cout << "yes" << endl;
        else
            cout << "no" << endl;
    }
    return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;

const int MAX=100005;
vector<int> S[MAX];

int par[MAX];
int root(int a){
    if(par[a]==a) return a;
    else return par[a]=root(par[a]);
}
void unite(int a,int b){
    if(root(a)!=root(b)) par[root(b)]=root(a);
}
bool check(int a,int b){
    return root(a)==root(b);
}

int main(){

    int N,M;cin>>N>>M;
    for(int i=0;i<N;i++){
        par[i]=i;
    }
    for(int i=0;i<M;i++){
        int a,b;cin>>a>>b;
        unite(a,b);
    }
    int Q;cin>>Q;
    for(int i=0;i<Q;i++){
        int a,b;cin>>a>>b;
        if(check(a,b)) cout<<"yes"<<endl;
        else cout<<"no"<<endl;
    }

}

C++: #include <bits/stdc++.h>
#define ll long long
#define INF 999999999
#define MOD 1000000007

using namespace std;

typedef pair<int,int>P;

const int MAX_N = 100000;

int par[MAX_N];
int rank[MAX_N];

void initial(int n){		//?????????
	for(int i=0;i<n;i++){
		par[i] = i;
		rank[i] = 0;
	}
}

int find(int x){		//??¨??????????±???????
	if(par[x] == x){
		return x;
	}else{
		return par[x] = find(par[x]);
	}
}

void unite(int x,int y){
	x = find(x);
	y = find(y);
	if(x == y) return;
	if(rank[x] < rank[y]){
		par[x] = y;
	}else{
		par[y] = x;
		if(rank[x] == rank[y])
			rank[x]++;
	}
}

bool same(int x,int y){
	return find(x) == find(y);
}

int main()
{
	int n,m,q;
	int a,b;
	cin >> n;
	cin >> m;
	initial(n);
	for(int i=0;i<m;i++){
		cin >> a;
		cin >> b;
		unite(a,b);
	}
	cin >> q;
	for(int i=0;i<q;i++){
		cin >> a;
		cin >> b;
		if(same(a,b)){
			cout << "yes\n";
		}else{
			cout << "no\n";
		}
	}
}

C++: #include <cstdio>
#include <queue>
#include <vector>

std::queue<int> q;
typedef struct{
	bool isVisited;
	std::vector<int> neighbors;
} node;

void bfs(node* nodes, int t){
	int id;
	while (!q.empty()){
		id = q.front();
		q.pop();
		if (!nodes[t].isVisited){
			for (int i=0; i<nodes[id].neighbors.size(); i++){
				if (!nodes[nodes[id].neighbors[i]].isVisited){
					q.push(nodes[id].neighbors[i]);
					nodes[nodes[id].neighbors[i]].isVisited=true;
				}
			}
		}
	}
	if (nodes[t].isVisited) printf("yes\n");
	else printf("no\n");
}

int main(){
	int n, d, num_relation, n_query, s, t;
	node *nodes;

	scanf("%d %d", &n, &num_relation);
	nodes = new node[n];
	for(int i=0;i<num_relation;i++){
		scanf("%d %d", &s, &t);
		nodes[s].neighbors.push_back(t);
		nodes[t].neighbors.push_back(s);
	}

	scanf("%d", &n_query);
	for(int i=0;i<n_query;i++){
		for (int j=0; j<n;j++){
			nodes[j].isVisited=false;
		}
		scanf("%d %d", &s, &t);
		q.push(s);
		bfs(nodes, t);
	}

	delete []nodes;
	return 0;
}