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;
public:
	Node(int id, int n);
	~Node(){ delete[] friends; }
	void addFriend(Node *friend_node);
	bool searchFriend(int id);
};

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

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

bool Node::searchFriend(int id)
{
	if (check_id == id) return false;
	check_id = id;

	if (this->id == id) {
		check_id = -1;
		return true;
	}

	for (int i = 0; i < friend_num; i++) {
		if (friends[i]->searchFriend(id)) {
			check_id = -1;
			return true;
		}
	}
	check_id = -1;
	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(t);
		if (result) cout << "yes" << endl;
		else cout << "no" << endl;
	}

	delete[] node;
	return 0;
}

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

bool x[10000][10000];
bool y[10000];

int main(){
	int n,m,a,b,q;
	cin>>n>>m;
	for(int i=0;i<m;i++){
		cin>>a>>b;
		x[a][b]=true;
		x[b][a]=true;
	}
	cin>>q;
	for(int h=0;h<q;h++){
		cin>>a>>b;
		memset(y,0,sizeof(y));
		y[a]=true;
		for(int i=0;i<50;i++){
			for(int j=0;j<n;j++){
				if(y[j]==true){
					for(int k=0;k<n;k++){
						if(x[j][k]==true){
							y[k]=true;
						}
					}
				}
				if(y[b]==true){
					cout<<"yes"<<endl;
					goto Exit;
				}
			}
		}
		cout<<"no"<<endl;
		Exit:;
	}
	return 0;
}

C++: #include <stdio.h>
#include <stack>
#include <vector> 
#include <iostream>
#define N 100000
using namespace std;

vector<int>  G[N];
int color[N];
int n;

void dfs(int s, int c)
{
    stack<int> st;
    color[s] = c;
    st.push(s);
    while(!st.empty())
    {
        int u = st.top();
        st.pop();
        for (int i = 0; i < G[u].size(); i++)
        {
            int v = G[u][i];
            if(color[v] == -1)
            {
                color[v] = c;
                st.push(v);
            }
        } 
    }
    return;
}

void assignColor()
{
    int id = 1;
    for (int i = 0; i < n; i++)
    {
        color[i] = -1;
    } 
    for (int u = 0; u < n; ++u)
    {
        if(color[u]==-1) dfs(u, id++);
    }

    return;
}

int main()
{
    //freopen("in3.txt","r",stdin);
    int m;
    scanf("%d %d",&n, &m);

    for (int i = 0; i < m; i++)
    {
        int s, t;
        scanf("%d %d",&s,&t); 
        G[s].push_back(t);
        G[t].push_back(s);
    } 

    assignColor(); 

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

C++: #include <stdio.h>
#include <iostream>
#include <utility>
#include <algorithm>
#include <math.h>
#include <vector>
#include <list>
#define N 100000
using namespace std;
int n;
list<int> adj[N];
bool f[N] = {};
int g[N] = {};


void setGraphNum(int v, int i)
{
    g[v] = i;
    f[v] = true;
    list<int>::iterator itr = adj[v].begin();
    while (itr != adj[v].end())
    {
        if (!f[*itr])
            setGraphNum(*itr, i);
        itr++;
    }
}
void CalcGraphNum()
{
    int k = 1;
    for (int i = 0; i < n; i++)
    {
        if (g[i] == 0)
            setGraphNum(i, k++);
    }
}

int main()
{
    int m, u, v, q;
    cin >> n >> m;

    for (int i = 0; i < m; i++)
    {
        cin >> u >> v;
        adj[u].push_back(v);
        adj[v].push_back(u);
    }

    CalcGraphNum();
    cin >> q;
    for (int i = 0; i < q; i++)
    {
        cin >> u >> v;
        if (g[u] == g[v])
            printf("yes\n");
        else
            printf("no\n");
    }

    return 0;
}

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

using namespace std;

bool* visit;

bool dfs(int s, int t, vector<vector<int>> sns) {
  if (s == t) {
    return true;
  }
  if (visit[s]) {
    return false;
  }

  visit[s] = true;

  int len = sns[s].size();
  for (int i = 0; i < len; i++) {
    int next = sns[s][i];
    if (dfs(next, t, sns)) {
      return true;
    }
  }
  return false;
}

int main() {
  int n,m,q,s,t;
  cin >> n >> m;

  vector<vector<int>> sns(n);
  
  for (int i = 0; i < m; i++) {
    cin >> s >> t;

    sns[s].push_back(t);
    sns[t].push_back(s);
  }

  cin >> q;
  for (int i = 0; i < q; i++) {
    cin >> s >> t;
    visit = new bool[n];
    if (dfs(s, t, sns)) {
      cout << "yes" << endl;
    } else {
      cout << "no" << endl;
    }
  }
  return 0;
}