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 <iostream>
using namespace std;

class Node{
private:
	int id;
	int friend_num;
	Node **friends;
	int check_id[2];
public:
	Node(int id, int n);
	~Node(){ delete[] friends; }
	void addFriend(Node *friend_node);
	bool searchFriend(int s_id, int t_id);
};

Node::Node(int id, int n)
{
	this->id = id;
	friend_num = 0;
	friends = new Node*[n];
	check_id[0] = check_id[1] = -1;
}

void Node::addFriend(Node *friend_node)
{
	friends[friend_num] = friend_node;
	friend_num++;
}

bool Node::searchFriend(int s_id, int t_id)
{
	if (check_id[0] == s_id && check_id[1] == t_id) return false;
	check_id[0] = s_id;
	check_id[1] = t_id;

	if (this->id == t_id) return true;

	for (int i = 0; i < friend_num; i++) {
		if (friends[i]->searchFriend(s_id, t_id)) return true;
	}

	return false;
}

int main(void)
{
	int n;
	cin >> n;	
	Node **node = new Node*[n];
	for (int i = 0; i < n; i++) node[i] = new Node(i, n);

	int m;
	cin >> m;
	for (int i = 0; i < m; i++) {
		int s, t;
		cin >> s >> t;
		node[s]->addFriend(node[t]);
		node[t]->addFriend(node[s]);
	}
		
	int q;
	cin >> q;
	for (int i = 0; i < q; i++) {
		int s, t;
		cin >> s >> t;
		bool result = node[s]->searchFriend(s, t);
		if (result) cout << "yes" << endl;
		else cout << "no" << endl;
	}

	delete[] node;
	return 0;
}

C++: #include <iostream>
#include <cmath>
#include <string>
#include <vector>
#include <algorithm>
#include <stack>
#include <queue>


using namespace std;

int *passed;

bool do_check(int s, int t, vector< vector<int> > a){
  queue<int> q;
  
  bool flag = false;
  if(s==t){flag=true;}
  q.push(s);
  while(q.size()>0 && flag==false){
    s = q.front();
    q.pop();
    for(int i=0;i<a[s].size();i++){
      int tmp = a[s].at(i);
      if(tmp == t){
	flag = true;
      }
      if(passed[tmp] == 0){
	passed[tmp] = 1;
	q.push(tmp);
      }
    }
  }
  return flag;
}

int main(){
  int n, m;
  cin >> n >> m;
  passed = new int[n];
  vector< vector<int> > a;

  for(int i=0;i<n;i++){
    vector<int> tmp;
    a.push_back(tmp);
  }

  for(int i=0;i<m;i++){
    int tmpa, tmp;
    cin >> tmpa >> tmp;
    a[tmpa].push_back(tmp);
    a[tmp].push_back(tmpa);
  }

  // Questions
  int q_num;
  cin >> q_num;
  // cout << "q_num: " << q_num << endl;
  for(int i=0;i<q_num;i++){
    for(int j=0;j<n;j++){
      passed[j]=0;
    }
    int s, t;
    cin >> s >> t;

    // cout << s << ": " << do_check(s, t, a) << endl;
    if(do_check(s, t, a)){
      cout << "yes" << endl;
    }else{
      cout << "no" << endl;
    }
  }
  
}

C++: #include<iostream>
#include<cstdio>
#include<cstring>
#include<string>
#include<algorithm>
#include<bitset>
#include<vector>
#include<deque>
#include<queue>
#include<map>
#include<set>
#include<stack>
#include<cmath>
#include<iomanip>
#include <functional>
using namespace std;
typedef long long ll;
const int mod = 1000000007;
const int INF = 1 << 28;
//cout << fixed << std::setprecision(9)
//memset(a, 0, sizeof(a));
//--------------------------


int n, m, q;
vector<int> g[100005];
int col[100005];

void dfs(int r, int c)
{
	stack<int> stk;
	stk.push(r);
	col[r] = c;

	while (!stk.empty()) {
		int u = stk.top(); stk.pop();
		for (int i = 0; i < g[u].size(); i++) {
			int v = g[u][i];
			if (col[v] == -1) {
				stk.push(v);
				col[v] = c;
			}
		}

	}
}

void solve()
{
	int c = 0;

	for (int i = 0; i < n; i++) {
		col[i] = -1;
	}

	for (int i = 0; i < n; i++) {
		if (col[i] == -1) {
			dfs(i, ++c);
		}
	}
}


int main()
{
	cin >> n >> m;
	for (int i = 0; i < m; i++) {
		int s, t;
		cin >> s >> t;
		g[s].push_back(t);
		g[t].push_back(s);
	}
	solve();
	cin >> q;
	for (int i = 0; i < q; i++) {
		int s, t;
		cin >> s >> t;
		if (col[s] == col[t]) {
			cout << "yes" << endl;
		}
		else {
			cout << "no" << endl;
		}
	}

	return 0;
}

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

int n, m;
stack<int> S;
vector<int> V[100000];
int color[100000];

void dfs(int i, int id){
    S.push(i);
    color[i] = id;

    while(!S.empty()){
        int u = S.top();
        S.pop();
        for(int i=0; i<V[u].size(); i++){
            int v = V[u][i];
            if(color[v]==-1){
                color[v] = id;
                S.push(v);
            }
        }
    }
}

void dfs_init(){

    int id = 1; //グラフの識別
    for(int i=0; i<n; i++){
        color[i] = -1;
    }
    for(int i=0; i<n; i++){
        if(color[i]==-1) dfs(i, id++);
    }
}

int main(){

    cin >> n >> m;

    for(int i=0; i<m; i++){
        int a, b;
        cin >> a >> b;
        V[a].push_back(b);
        V[b].push_back(a);
    }

    dfs_init();

    int q;
    cin >> q;
    for(int i=0; i<q; i++){
    int x, y;
    cin >> x >> y;
    if(color[x]==color[y]) cout << "yes" << endl;
    else cout << "no" << endl;
    }

    return 0;
}