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 <stdio.h>
#include <stack>
#include <iostream>
using namespace std;
int G[100000][100000];
int vis[100000];
int n;

bool dfs(int s, int t)
{
    if (G[s][t] == 1 || G[t][s] == 1) return true;
    vis[s] = 1;
    for (int i = 0; i < n; i++)
    {
        if (G[s][i] == 1 && vis[i] == 0)
            {
                bool a = (dfs(i,t)); 
                if(a) 
                {
                    vis[s] = 0;
                    return a;
                }
            }

    } 
    vis[s] = 0;
    return false;
}

int main()
{
    freopen("in3.txt","r",stdin);
    int m;
    scanf("%d %d",&n, &m);
    for (int i = 0; i < n; i++)
    {
        vis[i] = 0; 
    } 
    for (int i = 0; i < n; i++)
    {
        for (int j = 0; j < n; j++)
        {
            G[i][j] = 0; 
        }  
    } 
    for (int i = 0; i < m; i++)
    {
        int s, t;
        scanf("%d %d",&s,&t); 
        G[s][t] = 1;
        G[t][s] = 1;
    } 
    int q,s,t;
    scanf("%d",&q);
    for (int i = 0; i < q; i++)
    {
        scanf("%d %d",&s,&t);
        if(dfs(s,t)||dfs(t,s)) printf("yes\n");
        else printf("no\n");
    } 
    return 0;
}

C++: #include <iostream>
#include <vector>
#define N_MAX 100000
using namespace std;

vector<int> sns[N_MAX];
int* group;
int g = 0;

void dfs(int s) {
  if (group[s] != 0) return;
  group[s] = g;
  
  int len = sns[s].size();
  for (int i = 0; i < len; i++) {
    dfs(sns[s][i]);
  }
}

int main() {
  int n,m,q,s,t;
  cin >> n >> m;

  for (int i = 0; i < m; i++) {
    cin >> s >> t;

    sns[s].push_back(t);
    sns[t].push_back(s);
  }

  // dfs
  group = new int[n];
  for (int i = 0; i < n; i++) {
    if (group[i] == 0) {
      g++;
      dfs(i);
    }
  }

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

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

const int M = 10000000;

void connected_components(
  std::vector<std::vector<int> >& adj_list,
  std::vector<int>& component_numbers,
  int root, int current_component){
  assert(component_numbers[root] == M);

  std::queue<int> target_q;
  target_q.push(root);
  component_numbers[root] = current_component;
  // dist_q.push(0;)
  while(!target_q.empty()){
    int vtx = target_q.front(); target_q.pop();
    for(int const&  u : adj_list[vtx]){
      if(component_numbers[u] == M){
        target_q.push(u);
        component_numbers[u] = current_component;
      }
    }
  }
}

int main(int argc, char const *argv[]) {
  int n, m, q;
  std::cin >> n;
  std::cin >> m;

  std::vector<std::vector<int> > adj_list(n);

  for (size_t i = 0; i < m; i++) {
    int a, b;
    std::cin >> a;
    std::cin >> b;
    adj_list[a].push_back(b);
  }

  std::vector<int> component(n, M);

  for (size_t i = 0; i < n; i++) {
    if(component[i] == M){
      connected_components(adj_list, component, i, i);
    }
  }

  std::cin >> q;
  for(size_t i =0; i < q; i++){
    int a, b;
    std::cin >> a;
    std::cin >> b;
    bool in_same_component = (component[a] == component[b]);
    std::cout << (in_same_component ? "yes" : "no") << std::endl;
  }


  return 0;
}

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

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

    int link[n];
    std::vector<std::vector<int>> list;
    for (int i = 0; i < n; i++) {
        link[i] = -1;
    }

    int cnt = 0;
    int s, t;
    for (int i = 0; i < m; i++) {
        std::cin >> s >> t;
        if (link[s] == -1 && link[t] == -1) {
            link[s] = link[t] = cnt;
            cnt++;
            list.emplace_back(std::vector<int>({s, t}));
        } else if (link[s] == -1) {
            link[s] = link[t];
            list[link[t]].emplace_back(s);
        } else if (link[t] == -1) {
            link[t] = link[s];
            list[link[s]].emplace_back(t);
        } else if (link[s] < link[t]) {
            list[link[s]].insert(list[link[s]].end(), list[link[t]].begin(), list[link[t]].end());
            for (auto val : list[link[t]]) {
                link[val] = link[s];
            }
        } else if (link[t] < link[s]) {
            list[link[t]].insert(list[link[t]].end(), list[link[s]].begin(), list[link[s]].end());
            for (auto val : list[link[s]]) {
                link[val] = link[t];
            }
        }
    }

    int q;
    std::cin >> q;
    for (int i = 0; i < q; i++) {
        std::cin >> s >> t;
        if (link[s] == link[t] && link[s] != -1) {
            std::cout << "yes" << std::endl;
        } else {
            std::cout << "no" << std::endl;
        }
    }
}

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

int root(int x,int par[]){
    if (par[x] == x) return x;
    return par[x]=root(par[x],par);
}

int main(void){
    int n,m,q,s,t,i,rs,rt;
    cin>>n>>m;
    int par[100000];
    for(i=0;i<n;i++)par[i]=i;
    
    for(i=0;i<m;i++){
        cin>>s>>t;
        rs=root(s,par),rt=root(t,par);
        if(rs!=rt)par[rs]=rt;
    }

    for(i=0;i<n;i++){
        par[i]=root(i,par);
    }
    
    cin>>q;
    for(i=0;i<q;i++){
        cin>>s>>t;
        if(par[s]==par[t]){
            cout<<"yes"<<endl;
        }
        else{
            cout<<"no"<<endl;
        }
    }
    
    return 0;
}