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 <cstdio>
#include <vector>
#include <queue>

using namespace std;
#define MAX_N (100010)
int n;
int m;
int q;
vector<int> G[MAX_N];
int id[MAX_N];
int cur_id;

void bfs( int cur ) {
    queue< int > Q;
    Q.push( cur );
    id[cur] = cur_id;
    while ( !Q.empty() ) {
	int v = Q.front(); Q.pop();
	for ( int i = 0; i < G[v].size(); i++ ) {
	    int next = G[v][i];
	    if ( id[next] == -1 ) {
		id[next] = cur_id;
		Q.push( next );
	    }
	}
    }

    return;
}

int main()
{
    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 );
    }

    for ( int i = 0; i < n; i++ ) id[i] = -1;
    cur_id = 0;    

    for ( int i = 0; i < n; i++ ) {
	if ( id[i] == -1 ) { 
	    bfs( i );
	    cur_id++;
	}
    }

    scanf("%d", &q);


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

    return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;

int n,m;
vector<vector<int>> G(100005,vector<int>(0));
vector<int> color(100005,0);

void dfs(int u,int c){
    if(color[u]>0) return;
    color[u]=-1;
    for(int i=0;i<G[u].size();i++){
        if(color[G[u][i]]==0){
            dfs(G[u][i],c);
        }
    }
    color[u]=c;
}

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

    for(int i=0;i<n;i++){
        dfs(i,i+1);
    }

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

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(void){
  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<bits/stdc++.h>
using namespace std;
static const int MAX=100000;
static const int NIL=-1;
int n;
vector<int>G[MAX];//隣接リスト
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);
      }
    }
  }
}
int main(){
  int s,t,m,p;
  cin>>n>>m;
  for(int i=0;i<m;i++){
    cin>>s>>t;
    G[s].push_back(t);
    G[t].push_back(s);
  }
  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++);
    }
  }
  cin>>p;
  for(int i=0;i<p;i++){
    cin>>s>>t;
    if(color[s]==color[t]){
      cout<<"yes"<<endl;
    }else{
      cout<<"no"<<endl;
    }
  }
  return(0);
}