Go: package main

import (
	"bufio"
	"fmt"
	"log"
	"os"
	"strconv"
	"strings"
)

// Node 頂点
type Node struct {
	gid  int   // グループID
	edge []int // 隣接辺
}

// NoID グループIDなし
const NoID = -1

// NewNode 頂点の生成
func NewNode() *Node {
	return &Node{gid: NoID, edge: []int{}}
}

func parseNode(nodes []*Node, gid int, queue []int) {
	if len(queue) == 0 {
		return
	}
	var nextQ []int
	for _, id := range queue {
		node := nodes[id]
		if node.gid == NoID {
			node.gid = gid
			for _, edge := range node.edge {
				nextQ = append(nextQ, edge)
			}
		}
	}
	parseNode(nodes, gid, nextQ)
	return
}
func digNode(nodes []*Node, id, gid int) {
	node := nodes[id]
	if node.gid != NoID {
		// 探索済み
		return
	}
	node.gid = gid
	for _, edge := range node.edge {
		digNode(nodes, edge, gid)
	}
	return
}

func main() {
	scanner := bufio.NewScanner(os.Stdin)
	n, m := eGetInt2(scanner)

	nodes := make([]*Node, n)
	for i := 0; i < n; i++ {
		nodes[i] = NewNode()
	}

	for i := 0; i < m; i++ {
		a, b := eGetInt2(scanner)
		nodes[a].edge = append(nodes[a].edge, b)
		nodes[b].edge = append(nodes[b].edge, a)
	}

	for i := 0; i < n; i++ {
		// 幅優先探索
		// gid := i
		// queue := []int{i}
		// parseNode(nodes, gid, queue)

		// 深さ優先探索
		digNode(nodes, i, i)
	}

	q := eGetInt(scanner)
	for i := 0; i < q; i++ {
		a, b := eGetInt2(scanner)
		if nodes[a].gid == nodes[b].gid {
			fmt.Println("yes")
		} else {
			fmt.Println("no")
		}
	}
}

func eGetInt(scanner *bufio.Scanner) int {
	t := eAtoi(strings.Fields(eGetline(scanner)))
	return t[0]
}
func eGetInt2(scanner *bufio.Scanner) (int, int) {
	t := eAtoi(strings.Fields(eGetline(scanner)))
	return t[0], t[1]
}

func eGetline(p *bufio.Scanner) string {
	if !p.Scan() {
		if err := p.Err(); err != nil {
			log.Fatal(err.Error())
		}
		return ""
	}
	return p.Text()
}

func eAtoi(s []string) []int {
	ints := make([]int, len(s))
	var err error
	for i, e := range s {
		ints[i], err = strconv.Atoi(e)
		if err != nil {
			log.Fatal(err.Error())
		}
	}
	return ints
}

C++: #include <cassert>
#include <algorithm>
#include <iostream>
#include <vector>
#include <string>

class TVertex
{
    int FIndex;
    int FCommuniyId;
    std::vector<TVertex*> FList;

public:
    TVertex(int Index)
     : FIndex(Index), FCommuniyId(0)
    {}
    void AddPath(TVertex* Vertex)
    {
        FList.push_back(Vertex);
    }
    void SetCommunity(int CommunityId)
    {
        if(FCommuniyId) return;
        FCommuniyId = CommunityId;
        for(std::vector<TVertex*>::iterator It = FList.begin(); It != FList.end(); ++It){
            TVertex* V = *It;
            V->SetCommunity(CommunityId);
        }
    }
    int CommunityId()const
    {
        return FCommuniyId;
    }
};
class TGraph
{
    std::vector<TVertex*> FTable;
    void Init(int n)
    {
        assert(n > 0);
        FTable.resize(n);
        for(int i = 0; i < n; ++i){
            FTable[i] = new TVertex(i);
        }
    }
public:
    TGraph(int n)
    {
        Init(n);
    }
    
    void SetupVertex(std::istream& in)
    {
        int Index;
        in >> Index;
        assert(Index >= 1);
        assert(Index <= FTable.size());
        int k;
        in >> k;
        for(int i = 0; i < k; ++i){
            int v;
            in >> v;
            FTable[Index]->AddPath(FTable[v]);
        }
    }
    void MakeFriend(int s, int t)
    {
        assert(s < FTable.size());
        assert(t < FTable.size());
        FTable[s]->AddPath(FTable[t]);
        FTable[t]->AddPath(FTable[s]);
    }
    void SetCommunity()
    {
        for(std::size_t i = 0; i < FTable.size(); ++i){
            FTable[i]->SetCommunity(i+1);
        }
    }
    bool IsSameCommunity(int s, int t)const
    {
        assert(s < FTable.size());
        assert(t < FTable.size());
        return FTable[s]->CommunityId() == FTable[t]->CommunityId();
    }
};

int main()
{
    int n, m;
    std::cin >> n >> m;
    TGraph Graph(n);
    for(int i = 0; i < m; ++i){
        int s, t;
        std::cin >> s >> t;
        Graph.MakeFriend(s, t);
    }
    int q;
    std::cin >> q;
    Graph.SetCommunity();
    for(int i = 0; i < q; ++i){
        int s, t;
        std::cin >> s >> t;
        std::cout << (Graph.IsSameCommunity(s, t) ? "yes" : "no") << std::endl;
    }
    return 0;
    
}

C++: #include <cstdio>
#include <algorithm>
#include <vector>
#include <set>
using namespace std;

int main()
{
  int n, m, v1, v2;
  scanf("%d%d", &n, &m);
  vector<set<int>> v;
  set<int> s;

  for (int i = 0; i < m; i++)
  {
    scanf("%d%d", &v1, &v2);
    set<int> st = {v1, v2};
    vector<set<int>> ve;

    for (int j = 0; j < v.size(); j++)
    {
      s = v[j];
      if (s.find(v1) != s.end() || s.find(v2) != s.end())
        st.insert(s.begin(), s.end());
      else
        ve.push_back(s);
    }

    ve.push_back(st);
    v = ve;
  }

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

  for (int i = 0; i < q; i++)
  {
    scanf("%d%d", &v1, &v2);
    bool found = false;
    for (int j = 0; j < v.size() && !found; j++)
    {
      s = v[j];
      if (s.find(v1) != s.end() && s.find(v2) != s.end())
        found = true;
    }
    if (found)
      printf("yes\n");
    else
      printf("no\n");
  }

  return 0;
}

C++: #include <iostream>
#include<stdio.h>
#include<vector>
#include<stack>
#define MAX 100000

using namespace std;
vector<int> G[MAX];
int color[MAX], n;

void dfs_visit(int r, int id) { //???????????°
    stack<int> S;
    S.push(r);
    color[r] = id;
    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] == -1) {
                color[v] = id;
                S.push(v);
            }
        }
    }
}

void assignColor() { // ?????????????????°
    int id = 1;
    for(int i = 0; i < n; i++) {
        color[i] = -1;
    }
    for(int i = 0; i < n; i++) {
        if(color[i] == -1)
            dfs_visit(i, id++);
    }
}

int main()
{
    int m;
    scanf("%d%d", &n, &m);

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

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