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>

using namespace std;

struct UnionFind{
    UnionFind(int size):_array(size, -1){
    }

    bool same(int x, int y){
        return root(x) == root(y);
    }

    void unify(int x, int y){
        int rootx = root(x);
        int rooty = root(y);
        if( rootx == rooty ){
            return;
        }
        if( size(rootx) < size(rooty) ) swap(rootx,rooty);
        _array[rootx] += _array[rooty];
        _array[rooty] = rootx;
    }

    int root(int x){
        if( _array[x] < 0 ){
            return x;
        }
        return _array[x] = root(_array[x]);
    }

    int size(int x){
        return -_array[root(x)];
    }

    vector<int> _array;
};

void DFS(vector<vector<int>>& graph, int v, vector<int>& visited, int root, UnionFind& uf){
    visited[v] = true;
    uf.unify(v, root);
    for(int i = 0 ; i < graph[v].size(); i++){
        if(visited[graph[v][i]] == false){
            DFS(graph, graph[v][i], visited, root, uf);
        }
    }
}

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

    vector<vector<int>> graph(n);
    for(int i = 0; i < m; i++){
        int v1, v2;
        cin >> v1 >> v2;
        graph[v1].push_back(v2);
        graph[v2].push_back(v1);
    }

    vector<int> visited(n, false);
    UnionFind uf(n);

    for(int i = 0; i < n ; i++){
        if( visited[i] == false ){
            DFS(graph, i, visited, i, uf);
        }
    }

    int q;
    cin >> q;

    for(int i = 0; i < q; i++ ){
        int v1, v2;
        cin >> v1 >> v2;
        if( uf.same(v1, v2) ){
            cout << "yes" << endl;
        }else{
            cout << "no" << endl;
        }
    }

    return 0;

}

C++: //TLEになってしまった

#include<iostream>
#include<vector>
#include<utility>
using namespace std;
#define INF 1000000000

void dfs(vector< vector<int> >& rel,vector<int>& v,int c,int k){
  int l=rel[k].size();
  for(int i=0;i<l;i++){
    if(v[rel[k][i]]==0){
      v[rel[k][i]]=c;
      dfs(rel,v,c,rel[k][i]);
    }
  }
}


int main(){
  int n,m;cin >> n >> m;
  vector<int> v(n,0);//番号を記録(訪問済みでない場合は0)
  vector< vector<int> > rel(n);//隣接リスト

  //隣接リスト、Nodeの行列を作る必要ない
  for(int i=0;i<m;i++){
    int x,y;cin >> x >> y;
    rel[x].push_back(y);rel[y].push_back(x);
  }

  int col=0;
  for(int i=0;i<n;i++){
    if(v[i]==0){
      col++;
      dfs(rel,v,col,i);
    }
  }

  int q;cin >>q;
  for(int i=0;i<q;i++){
    int s,t;cin >> s >> t;
    //非連結だと0だろ
    if(v[s]==0 or v[s]!=v[t]) cout << "no" << endl;
    else cout << "yes" << endl;
  }
  # if 0
  for(int i=0;i<n;i++){cout <<  v[i] << " ";}
  cout << endl;
  # endif
}