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 <vector>
#include <queue>
#include <set>
using namespace std;

int main(){
  int n,m,q,a,b,s,t,k,h;
  vector<int> g[100001];
  queue<int> qu;
  set<int> ch;
  cin>>n>>m;
  for(int i=0;i<m;i++){
    cin>>a>>b;
    g[a].push_back(b);
    g[b].push_back(a);
  }
  cin>>q;
  for(int i=0;i<q;i++){
    cin>>s>>t;
    
    k=0; 
    ch.clear();
    while(qu.size()){
      qu.pop();
    }
    qu.push(s);
    
    while(qu.size()){//?????????
      n=qu.front();qu.pop();
      
      for(int j=0;j<g[n].size();j++){//????????????????????´????????????
	if(g[n][j]==t){
	  cout<<"yes"<<endl;
	  k++;
	  break;
	}
	if(ch.count(g[n][j])==0 ){
	  qu.push(g[n][j]);
	  ch.insert(g[n][j]);
	}
      }
      if(k>=1)break;
    }
    
    if(k==0)cout<<"no"<<endl;
  }
  return 0;
}

C++: #include<iostream>
#include<vector>
#include<stack>
using namespace std;
static const int MAX=100000;
static const int NIL=-1;
int n;
vector<int> G[MAX];
int color[MAX];
void dfs(int r,int c){
    stack<int> S;
    S.push(r);
    color[r]=c;
    while(!S.empty()){
        int u=S.top();
        S.pop();
        for(int i=0;i<G[u].size();i++){
            int v=G[u][i];
            if(color[v]==NIL){
                color[v]=c;
                S.push(v);
            }
        }
    }
}
void assignColor(){
    int id=1;
    for(int i=0;i<n;i++)color[i]=NIL;
    for(int i=0;i<n;i++){
        if(color[i]==NIL)
            dfs(i,id++);
    }
}
int main(){
    int s,t,m,q;
    cin>>n>>m;
    for(int i=0;i<m;i++){
        cin>>s>>t;
        G[s].push_back(t);
        G[t].push_back(s);
    }
    assignColor();
    cin>>q;
    for(int i=0;i<q;i++){
        cin>>s>>t;
        if(color[s]==color[t]) cout<<"yes"<<"\n";
        else cout<<"no"<<"\n";
    }
    return 0;
}

C++: #include<iostream> 
#include<vector> 
#include<stack>
using namespace std;
static const int MAX = 100000;
static const int NIL = -1;

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

void dfs(int r, int c){

  stack<int> S;
  S.push(r);
  color[r] = c;
  while(!S.empty()){
    int u = S.top(); S.pop();
    for(int i = 0;i < G[u].size();i++){
      int v = G[u][i];
      if(color[v] == NIL){
        color[v] = c;
        S.push(v);
      }
    }
  }
}

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

int main(){
  int s, t, m, q;

  cin >> n >> m;

  for(int i = 0;i < m;i++){
    cin >> s >> t;
    G[s].push_back(t);
    G[t].push_back(s);
  }

  assignColor();

  cin >> q;

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

  return 0;
}

C++: #include <stdio.h>
#include <stack>
#include <iostream>
using namespace std;
int G[10000][10000];
int vis[100000];
int n;

bool dfs(int s, int t)
{
    if (G[s][t] == 1 || G[t][s] == 1) return true;
    vis[s] = 1;
    for (int i = 0; i < n; i++)
    {
        if (G[s][i] == 1 && vis[i] == 0)
            {
                bool a = (dfs(i,t)); 
                if(a) 
                {
                    vis[s] = 0;
                    return a;
                }
            }

    } 
    vis[s] = 0;
    return false;
}

int main()
{
    //freopen("in3.txt","r",stdin);
    int m;
    scanf("%d %d",&n, &m);
    for (int i = 0; i < n; i++)
    {
        vis[i] = 0; 
    } 
    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 s, t;
        scanf("%d %d",&s,&t); 
        G[s][t] = 1;
        G[t][s] = 1;
    } 
    int q,s,t;
    scanf("%d",&q);
    for (int i = 0; i < q; i++)
    {
        scanf("%d %d",&s,&t);
        if(dfs(s,t)||dfs(t,s)) printf("yes\n");
        else printf("no\n");
    } 
    return 0;
}

C++: #include<stdio.h>
#include<queue>

using namespace std;

const int MAX = 100000;

int parent(int table[], int child) {

	while (table[child] != -1) {
		q.push(child);
		child = table[child];
	}
	return child;
}

int main() {
	int n, m, q;
	int table[MAX];

	scanf("%d %d", &n, &m);

	for (int i = 0; i < n; i++)table[i] = -1;
	for (int i = 0; i < m; i++) {
		int s, t;
		scanf("%d %d", &s, &t);
		
		int ps = parent(table, s);
		int pt = parent(table, t);
		if (ps != pt) {
			table[ps] = pt;
		}
	}

	scanf("%d", &q);

	for (int i = 0; i < q; i++) {
		int s, t;
		
		scanf("%d %d", &s, &t);

		int ps = parent(table, s);
		int pt = parent(table, t);

		if (ps == pt) {
			printf("yes\n");
		}
		else {
			printf("no\n");
		}
	}
	return 0;
}