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 <unordered_set>
#include <unordered_map>
#include <algorithm>
//#include "../cxx-prettyprint/prettyprint.hpp"

std::vector<std::vector<int>> Adj;
std::unordered_set<int> nodes_unvisited;
std::unordered_map<int, int> node_component_map;

void mark_nodes(int node, int component_id) {
    node_component_map[node] = component_id;
    nodes_unvisited.erase(node);
    for (int& next : Adj[node]) {
        if (nodes_unvisited.find(next) != nodes_unvisited.end()) {
            mark_nodes(next, component_id);
        }
    }
}

int main() {
    int n, m;
    std::cin >> n >> m;

    Adj.assign(n, std::vector<int>());
    for (int i = 0; i < m; i++) {
        int s, t;
        std::cin >> s >> t;
        Adj[s].push_back(t);
        Adj[t].push_back(s);
    }

    for (int i = 0; i < n; i ++) {
        nodes_unvisited.insert(i);
    }

    int component_id = 0;
    while (!nodes_unvisited.empty()) {
        int start = *nodes_unvisited.begin();
        mark_nodes(start, component_id);
        component_id ++;
    }

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

C++: #include <cstdio>
#include <vector>
#include <queue>
using namespace std;
static const int NIL = -1;

int n, m;
int *color;
vector<int> *v;

void bfs(int r, int c) {
    queue<int> q;
    q.push(r);
    while (!q.empty()) {
        int u = q.front();
        q.pop();
        if (color[u] == NIL) {
            color[u] = c;
        }
        for (vector<int>::iterator it = v[u].begin(); it != v[u].end(); it++) {
            if (color[*it] == NIL) {
                q.push(*it);
            }
        }
    }
}

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

int main() {
    scanf("%d %d", &n, &m);
    v = new vector<int>[n];

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

    assignColor();

    int q;
    scanf("%d", &q);

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

    return 0;
}

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

using namespace std;

int main() {
  vector<int> R[100000];
  queue<int> Q;
  int n,m,s,t,q;
  int visit[100000];

  cin >> n >> m;
  for(int i=0;i<m;i++){
    cin >> s >> t;
    R[s].push_back(t);
    R[t].push_back(s);
  }
  
  for(int j=0;j<n;j++) visit[j] = 0;
  for(int i=0;i<n;i++){
    if(visit[i] == 0){
      Q.push(i);
      while(Q.empty() == false){
	int u = Q.front();
	Q.pop();
	visit[u] = 1;
	for(int j=0;j<R[u].size();j++){
	  int v = R[u][j];
	  if(visit[v]==0)Q.push(v);
	}
	R[u].clear();
	R[u].push_back(i);
      }
    }
  }
    
  cin >> q;
  for(int i=0;i<q;i++){
    cin >> s >> t;
    if(R[s][0] == R[t][0]) cout << "yes" << endl;
    else cout << "no" << endl;
  }


  return 0;
}