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<stdio.h>
#include<queue>

#define MAX 100000

//int G[MAX+1][MAX+1];
int n, m;
std::queue<int> Q;

//bool bfs(int src, int dest) {
//    bool C[MAX];
//    for (int i = 0; i < n; ++i) C[i] = false;
//
//    Q.push(src);
//    while(!Q.empty()) {
//        int cur = Q.front();Q.pop();
//        for (int i = 0; i < n; ++i) {
//            if (G[cur][i] == 0) continue;
//            if (C[i]) continue;
//            if (i == dest) return true;
//            Q.push(i);
//            C[i] = true;
//        }
//    }
//
//    return false;
//}

int main() {
    //scanf("%d %d", &n, &m);
    //for (int i = 0; i < n; ++i) {
    //    for (int j = 0; j < n; ++j) {
    //        G[i][j] = 0;
    //    }
    //}
    //for (int i = 0; i < m; ++i) {
    //    int u,k;
    //    scanf("%d %d", &u, &k);
    //    G[u][k] = 1;
    //    G[k][u] = 1;
    //}

    //int q;
    //scanf("%d", &q);
    //for (int i = 1; i <= q; ++i) {
    //    int s,d;
    //    scanf("%d %d", &s, &d);
    //    bfs(s, d) ? printf("yes\n") : printf("no\n");
    //}

    return 0;
}

C++: #include <bits/stdc++.h>
#define rep(i, n) for (int i = 0; i < n; ++i)
#define FOR(i, a, b) for (int i = a; i < b; ++i)
#define ALL(vec) vec.begin(), vec.end()
#define rALL(vec) vec.rbegin(), vec.rend()
using namespace std;
using ll = long long;

vector<vector<int>> A;
vector<int> color;
int num = 1;

void dfs(int u) {
    stack<int> S;
    S.push(u);
    color[u] = num;
    while (!S.empty()) {
        int now = S.top(); S.pop();
        rep(i, A[now].size()) {
            int next = A[now][i];
            if (color[next] == -1) {
                color[next] = num;
                S.push(next);
            }
        }
    }
    num += 1;
}

int main() {
    int n, m;
    cin >> n >> m;
    A = vector<vector<int>>(n);
    color = vector<int>(n, -1);
    rep(i, m) {
        int s, t;
        cin >> s >> t;
        A[s].push_back(t);
        A[t].push_back(s);
    }
    rep(i, n) {
        if (color[i] == -1) dfs(i);
    }
    int q;
    cin >> q;
    rep(i, q) {
        int s, t;
        cin >> s >> t;
        if (color[s] == color[t]) cout << "yes" << endl;
        else cout << "no" << endl;
    }
    return 0;
}

C++: /**
 */

/*
 * test case 1
 2 1 1 2 1 1 2  
 test case 2
 4 4 1 2 1 3 2 4 3 4 1 1 2   
 */


#include <iostream>
#include <vector>
#include <queue>
using namespace std;
vector< vector<int> > rel;
vector<bool> visited;
int n, m, q;
int dest = 0;


bool fre1(int j) 
{
	for (int i=0;i<rel[j].size();i++)
	{
		int kk = rel[j][i];
		if (kk==dest) return true;
		if (visited[kk])continue;
		visited[kk]=true;
		if(fre1(kk))return true;
	}
	return false;
}

/**
 * preserve a priority que of nodes with the most connections. 
 * if there is a node with only 2 connections go look for the other one.
 */

priority_queue< pair<int, int> > pq;


bool fre3(int start) 
{
	for (int i=0;i<rel[start].size();i++)
	{
		int cand = rel[start][i];
		if (cand==dest) return true;
		if (visited[cand])continue;
		visited[cand]=true;
		int point = rel[cand].size();
		if (point == 1) continue;
		if (point == 2) {
			if (fre3(cand)) return true;
		} else {
			pq.push(pair<int, int>(point, cand));
		}
	}
	return false;
}


bool fre2(int start) 
{
	pq.push(pair<int,int>(0, start));
	while (pq.size())
	{
		pair<int, int> p = pq.top();
		pq.pop();
		start = p.second;
		if (fre3(start)) return true;
	}
	return false;
}


int main()
{
	cin >> n;
	rel.resize(n+1);
	cin >> m;
	for (int i=1;i<=m;i++){
		int j, k;
		cin >> j >> k;
		rel[j].push_back(k);
		rel[k].push_back(j);
	}

	cin >> q;
	for (int i=1;i<=q;i++){
		int start;
		cin >> start >> dest;
		visited.clear();
		visited.resize(n+1);
		cout << (fre2(start) ? "yes" : "no") << endl;
	}

	return 0;
}

C++: #include<iostream>
#include<vector>
using namespace std;

vector<int> par(100005,-1);

void initialize(int n){
	for (int i=0;i<n;i++){
		par[i]=i;
	}
	return;
}

int root(int x){
	if (x==par[x]){
		return x;
	}else{
		return par[x]=root(par[x]);
	}
}

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

void uni(int x,int y){
	x=root(x);
	y=root(y);
	if(x==y){
		return;
	}else{
		par[x]=y;
	}
}

int main(){
	int n,m,q,i,j;
	int s,t;
	
	cin >> n >> m;
	
	initialize(n);
	
	for(i=0;i<m;i++){
		cin >> s >> t;
		uni(s,t);
	}
	
	cin >> q;
	
	for (i=0;i<q;i++){
		cin >> s >> t;
		if (find(s,t)){
			cout << "yes" <<endl;
		}else{
			cout << "no" <<endl;
		}
	}
	return 0;
}