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 <bits/stdc++.h>
using namespace std;
int n, m;
vector< vector<int> > v;
vector<bool> used;

bool dfs(int pos, int dest){
  if(used[pos]) return false;
  used[pos] = true;
  if(pos == dest) return true;
  for(int i = 0; i < v[pos].size(); i++){
    if(dfs(v[pos][i], dest)){
      return true;
    }
  }
  return false;
}

int main(void){
  ios::sync_with_stdio(false);
  cin.tie(0);

  cin >> n >> m;
  v = vector< vector<int> >(n, vector<int>(0));
  used = vector<bool>(n, false);
  for(int i = 0; i < m; i++){
    int a, b; cin >> a >> b;
    v[a].push_back(b);
    v[b].push_back(a);
  }
  int q; cin >> q;
  for(int i = 0; i < q; i++){
    used = vector<bool>(n, false);
    int a, b; cin >> a >> b;
    if(dfs(a, b)){
      cout << "yes" << endl;
    }else{
      cout << "no" << endl;
    }
  }
  return 0;
}

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

const int MAX = 100000;
vector<int> G[MAX];

class DisjointSet{
public:
    vector<int> rank, parent;
    DisjointSet();
    DisjointSet(int size){
        rank.resize(size,0);
        parent.resize(size,0);
        for (int i=0; i<size; i++) {
            makeSet(i);
        }
    }

    bool same(int u,int v){
        if (parent[u] == parent[v]) {
            return true;
        }else{
            return false;
        }
    }
    
    void unite(int u,int v){
        int x = findSet(u);int y= findSet(v);
        if(rank[x]<rank[y]){
            parent[x] = y;
        }else{
            parent[y] = x;
            if(rank[x]==rank[y]){
                rank[x]++;
            }
        }
    }
    // ????????????????????????
    int findSet(int u){
        
        if(u!=parent[u])
            parent[u] = findSet(parent[u]);
        
        return parent[u];
    }
private:
    void makeSet(int i){
        rank[i] = 0;
        parent[i] = i;
    }
};
    
int main(int argc, const char * argv[]) {
    
    int n,m;
    cin >> n >> m;
    DisjointSet ds(n);
    
    for(int i=0;i<m;i++){
        int s,t;
        cin >> s >> t;
        ds.unite(s, t);
    }
    int q;
    cin >> q;
    for(int i=0;i<q;i++){
        int s,t;
        if(ds.same(s, t)) cout << "yes" << endl;
        else cout << "no" << endl;
    }
    return 0;
}