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<stack>
static const int MAX=100000;
static const int NIL=-1;

int n;
std::vector<int> G[MAX];
int color[MAX];
void DFS(int,int);
void assignColor(void);

int main(){
  int s, t, m, q;
  std::cin >> n >> m;
  for(int i=0; i<m; i++){
    std::cin >> s >> t;
    G[s].push_back(t);
    G[t].push_back(s);
  }
  assignColor();
  std::cin >> q;
  for(int i=0; i<q; i++){
    std::cin >> s >> t;
    if(color[s] == color[t]) std::cout << "yes\n";
    else std::cout << "no\n";
  }
  return 0;
}
void assignColor(void){
  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++);
}
void DFS(int r, int c){
  std::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);
      }
    }
  }
}

C++: #include<bits/stdc++.h>
using namespace std;
#define MOD 1000000007
#define NIL -1

int c = 0,n,m;
int color[100000];
vector<int> li[100000];

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 < li[u].size();i++) {
      if(color[li[u][i]] == NIL) {
        S.push(li[u].at(i));
        color[li[u][i]] = c;
      }
    }
  }
}

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



int main() {

  
  cin >> n >> m;


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

  for(int i = 0;i < n;i++) {
    color[i] = NIL;
  }

  int q;
  cin >> q;

  assignColor();

  for(int i = 0;i < q;i++) {
    int a,b;
    cin >> a >> b;
    cout << ((color[a] == color[b]) ? "yes" : "no") << endl;
  }


}

C++: #include <stdio.h>
#define N 100000

int a[N]={};

int search(int c)
{
	if(c==a[c]) return c;
	
	return a[c]=search(a[c]);
}

int main(void)
{
 int i,n,m,q,s,t;

 for(i=0;i<N;i++) a[i]=i;

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

 for(i=0;i<m;i++){

  scanf("%d %d",&s,&t);

  if(search(s)==search(t)) a[t]=s;

 }

 scanf("%d",&q);

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

  if(search(s)==search(t)) printf("yes\n");
  else printf("no\n");

 }

 return 0;
}

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

vector<int> list[100000];
int n,m;

bool bfs(int s, int t){
  bool used[m];
  for(int i=0;i<m;i++) used[i]=false;
  queue<int> Q;
  Q.push(s); used[s]=true;
  while(!Q.empty()){
    int k=Q.front(); Q.pop();
    if(k==t){return true;}
    for(int i=0;i<list[k].size();i++){
      int temp=list[k][i];
      if(!used[temp]){
        Q.push(temp); used[temp]=true;
      }
    }
  }
  return false;
}
int main(){
  cin>>n>>m;
  for(int i=0;i<m;i++){
    int u,v; cin>>u>>v;
    list[u].push_back(v);
    list[v].push_back(u);
  }
  int q; cin>>q;
  for(int i=0;i<q;i++){
    int s,t; cin>>s>>t;
    if(bfs(s, t)){
      cout<<"yes"<<"\n";
    }else{
      cout<<"no"<<"\n";
    }
  }
}