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 <algorithm>
#include <cmath>
#include <climits>

using namespace std;

const int WHITE=0, GRAY=1, BLACK=2;

struct DFS {
    int n;
    vector<vector<int>> g;
    vector<int> group;
    vector<int> state;
    int groupId = 0;
    
    DFS(int n):n(n) {
        g.assign(n, vector<int>());
        group.assign(n, -1);
        state.assign(n, WHITE);
    }
    
    void addEdge(int u, int v) {
        g[u].push_back(v);
    }
    
    void solve() {
        for (int i = 0; i < n; i++) {
            if (state[i] == WHITE) {
                groupId++;
                dfs(i);
            }
        }
    }
    
    void dfs(int u) {
        state[u] = GRAY;
        group[u] = groupId;
        for (int v : g[u]) {
            if (state[v] == WHITE) {
                dfs(v);
            } 
        }
        state[u] = BLACK;
    }
    
    void print() {
        for (int i = 0; i < n; i++) {
            cout << i << ":";
            for (int v : g[i]) {
                cout << v << " ";
            }
            cout << endl;
        }
    }
};

int main() {
    ios::sync_with_stdio(false);
    int n, e;
    cin >> n >> e;
    
    DFS dfs(n);
    
    for (int i = 0; i < e; i++) {
       int u, v;
       cin >> u >> v;
       dfs.addEdge(u, v);
       dfs.addEdge(v, u);
    }
   
    dfs.solve();
    
    int q;
    cin >> q;
    
    for (int i = 0; i < q; i++) {
        int u, v;
        cin >> u >> v;
        if (dfs.group[u] == dfs.group[v]) {
            cout << "yes" << endl;
        }
        else {
            cout << "no" << endl;
        }
    }
    
    return 0;
}

C++: #include <iostream>
#include <vector>
#include <stack>
#define MAX 100000
using namespace std;
int n,m;
vector<vector<int> > list(MAX);
int grp[MAX];
int group;

void dfs(int now){
	stack<int> next;
	grp[now]=group;	next.push(now);
	while(!next.empty()){
		now=next.top();	next.pop();
		for(int i=0;i<(int)list[now].size();i++){
			if(grp[list[now][i]]==-1){
				grp[list[now][i]]=group;
				next.push(list[now][i]);
			}
		}
	}
}

int main(){
	cin>>n>>m;
	int s,t;
	for(int i=0;i<m;i++){
		cin>>s>>t;
		list[s].push_back(t);
		list[t].push_back(s);
	}
	for(int i=0;i<n;i++)	grp[i]=-1;
	group=1;
	for(int i=0;i<n;i++){
		if(grp[i]==-1){
			dfs(i);
			group++;
		}
	}
	int q;	cin>>q;
	for(int i=0;i<q;i++){
		cin>>s>>t;
		if(grp[s]==grp[t])	cout<<"yes"<<endl;
		else 	cout<<"no"<<endl;
	}
	return 0;
}

C++: #include <string>
#include <vector>
#include <stack>
#include <iostream>
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 <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;
}