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 <stack>
using namespace std;

const long N = 100;
const long WHITE = 0;
const long GRAY = 1;
const long BLACK = 2;
const long NIL = -1;

long n, M[N][N];
long color[N], cc[N], cp = 0;
long nt[N];

long next(long u){
	for (long v = nt[u]; v <= n; v++){
		nt[u] = v + 1;
		if (M[u][v]) return v;
	}
	return -1;
}

void dfs_visit(long r){
	for (long i = 0; i < n; i++) nt[i] = 0;

	stack<long> S;
	S.push(r);
	color[r] = GRAY;
	if (cc[r] == NIL) cc[r] = cp;

	while (!S.empty()){
		long u = S.top();
		long v = next(u);
		if (v != -1){
			if (color[v] == WHITE){
				color[v] = GRAY;
				if (cc[v] == NIL) cc[v] = cp;
				S.push(v);
			}
		}
		else {
			S.pop();
			color[u] = BLACK;
		}
	}
	cp++;
}

void dfs(){
	for (long i = 0; i < n; i++){
		color[i] = WHITE;
		nt[i] = 1;
	}

	for (long u = 0; u < n; u++){
		if (color[u] == WHITE) dfs_visit(u);
	}

}

int main(){
	long m, q;
	cin >> n >> m;
	for (long i = 0; i < n; i++){
		cc[i] = NIL;
		for (long j = 0; j < n; j++){
			M[i][j] = 0;
		}
	}
	for (long i = 0; i < m; i++){
		long s, t;
		cin >> s >> t;
		M[s][t] = M[t][s] = 1;
	}
	dfs();
	cin >> q;
	for (long i = 0; i < q; i++){
		long s, t;
		cin >> s >> t;
		if (cc[s] == cc[t]) cout << "yes" << endl;
		else cout << "no" << endl;
	}

	return 0;
}

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

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

void dfs(node* nodes, int id, int t){

	for (int i=0; i<nodes[id].neighbors.size(); i++){
		if (nodes[t].isVisited) break;
		if (!nodes[nodes[id].neighbors[i]].isVisited){
			nodes[nodes[id].neighbors[i]].isVisited=true;
			dfs(nodes, nodes[id].neighbors[i], t);
		}
	}
}

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);
		dfs(nodes, s, t);
		if (nodes[t].isVisited) printf("yes\n");
		else printf("no\n");

	}

	delete []nodes;
	return 0;
}

C++: #include<cstdio>
#include<vector>
#include<algorithm>
#include<utility>
#include<numeric>
#include<iostream>
#include<array>
#include<string>
#include<sstream>
#include<stack>
#include<queue>
#include<list>
#define _USE_MATH_DEFINES

#include<math.h>
#include<map>

#define SENTINEL 1000000001

#define min(a,b) (a)>(b)?(b):(a)
#define max(a,b) (a)>(b)?(a):(b)

using namespace std;

int from[100000];
int to[100000];

bool checked[100000];

bool judge(int f, int t,int m)
{
	if (checked[f])
	{
		return false;
	}

	checked[f] = true;

	bool isFriend = false;
	for (int i = 0; i < m; i++)
	{
		if (from[i] == f)
		{
			if (to[i] == t)
			{
				isFriend = true;
			}
			else
			{
				isFriend = judge(to[i], t, m);
			}
			if (isFriend)
			{
				break;
			}
		}
		if (to[i] == f)
		{
			if (from[i] == t)
			{
				isFriend = true;
			}
			else
			{
				isFriend = judge(from[i], t, m);
			}
			if(isFriend)
			{
				break;
			}
		}
	}
	return isFriend;
}

int main()
{
	int n, m;
	cin >> n >> m;

	for (int i = 0; i < m; i++)
	{
		int f, t;
		cin >> f >> t;

		from[i] = f;
		to[i] = t;
	}

	int q;
	cin >> q;

	for (int i = 0; i < q; i++)
	{
		int f, t;
		cin >> f >> t;

		for (int i = 0; i < n; i++)
		{
			checked[i] = false;
		}

		printf(judge(f, t, m) ? "yes\n" : "no\n");
	}
	return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define P pair<ll,ll>
#define FOR(I,A,B) for(ll I = (A); I < (B); ++I)
#define POSL(x,v) (lower_bound(x.begin(),x.end(),v)-x.begin()) //ai>=v  x is sorted
#define POSU(x,v) (upper_bound(x.begin(),x.end(),v)-x.begin()) //ai>v  x is sorted
#define NUM(x,v) (POSU(x,v)-POSL(x,v))  //x is sorted
#define SORT(x) (sort(x.begin(),x.end())) // 0 2 2 3 4 5 8 9
#define REV(x) (reverse(x.begin(),x.end())) //reverse
#define TO(x,t,f) ((x)?(t):(f))
#define CLR(mat) memset(mat, 0, sizeof(mat))
#define FILV(x,a) fill(x.begin(),x.end(),a)
#define FILA(ar,N,a) fill(ar,ar+N,a)
#define NEXTP(x) next_permutation(x.begin(),x.end())
ll gcd(ll a,ll b){if(a<b)swap(a,b);if(a%b==0)return b;else return gcd(b,a%b);}
ll lcm(ll a,ll b){ll c=gcd(a,b);return ((a/c)*(b/c)*c);}//saisyo kobaisu
#define pb push_back
#define pri(aa) cout<<(aa)<<endl
#define mp(x,y) make_pair(x,y)
#define fi first
#define se second
const ll INF=1e18+7;
const ll MOD=1e9+7;
const ll N = 1007;
class UnionFind{
public:
	vector<int> par;
	//0-indexed
	void init(int n = 1) {
		par.resize(n);
		for (int i = 0; i < n; ++i) par[i] = i;
	}
	int root(int x = 1){
		if(par[x]==x)return x;
		else{
			return par[x] = root(par[x]);
		}
	}
	void unite(int x = 1,int y = 1){
		x = root(x);
		y = root(y);
		if(x==y)return;
		else par[x] = y;
	}
};
int main(){
	ios::sync_with_stdio(false);
	cin.tie(0);
	ll n,m;
	cin>>n>>m;
	UnionFind uf;
	uf.init(n);
	FOR(i,0,m){
		ll x,y;
		cin>>x>>y;
		uf.unite(x,y);
	}
	ll q;
	cin>>q;
	FOR(i,0,q){
		ll x,y;
		cin>>x>>y;
		if(uf.root(x)==uf.root(y)){
			pri("yes");
		}else{
			pri("no");
		}
	}
}