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 <iostream>
#include <vector>
#include <queue>
using namespace std;

vector<int> list[100000];
int n,m;

bool bfs(int s, int t){
  bool used[m];
  for(int i=0;i<m;i++) used[i]=false;
  queue<int> Q;
  Q.push(s); used[s]=true;
  while(!Q.empty()){
    int k=Q.front(); Q.pop();
    if(k==t){return true;}
    for(int i=0;i<list[k].size();i++){
      int temp=list[k][i];
      if(!used[temp]){
        Q.push(temp); used[temp]=true;
      }
    }
  }
  return false;
}
int main(){
  cin>>n>>m;
  for(int i=0;i<m;i++){
    int u,v; cin>>u>>v;
    list[u].push_back(v);
    list[v].push_back(u);
  }
  int q; cin>>q;
  for(int i=0;i<q;i++){
    int s,t; cin>>s>>t;
    if(bfs(s, t)){
      cout<<"yes"<<"\n";
    }else{
      cout<<"no"<<"\n";
    }
  }
}

C++: #include <iostream>
#include <string>
#include <vector>
#include <stack>
using namespace std;
#define N 100000
#define WHITE 0
#define GRAY 1
#define BLACK 2

vector<int> G[100];
int color[N], num_members;
int cnt[N];

string dfs(int r, int target) {
    stack<int> S;
    S.push(r);
    color[r] = GRAY;

    while(!S.empty()) {
        int u = S.top();
        int v = G[u][cnt[u]];
        if(u==target) {
            return "yes";
        }
        cnt[u]++;

        if(v!=-1) {
            if(color[v]==WHITE) {
                color[v] = GRAY;
                S.push(v);
            }
        }
        else {
            S.pop();
            color[u] = BLACK;
        }
    }

    return "no";
}

int main() {
    int num_relations, from_id, to_id;
    int num_tests, test_from_id, test_to_id;

    cin >> num_members >> num_relations;
    for(int i=0; i<num_relations; i++) {
        cin >> from_id >> to_id;
        G[from_id].push_back(to_id);
    }
    //最後に番兵的な何かを仕込んでおく
    for(int i=0; i<num_members; i++) {
        G[i].push_back(-1);
    }

    cin >> num_tests;
    for(int i=0; i<num_tests; i++) {
        for(int j=0; j<num_members; j++) {
            color[j] = WHITE;
            cnt[j] = 0;
        }
        cin >> test_from_id >> test_to_id;
        cout << dfs(test_from_id, test_to_id) << endl;
    }
    
    return 0;
}

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

struct Node {
  vector<int> friends;
  int depth;
};
vector<Node> nodes;


void bfs(int id) {
  queue<int> q;
  q.push(id);

  for (auto el : nodes) {
    el.depth = -1;
  }
  nodes[id].depth = 0;

  while (!q.empty()) {
    int u = q.front();
    q.pop();
    for (auto fid : nodes[u].friends) {
      if (nodes[fid].depth <= 0) {
        q.push(fid);
        nodes[fid].depth = nodes[u].depth + 1;
      }
    }
  }
}

bool isAccessible(int id){
  return (nodes[id].depth > 0);
}


int main() {
  int nrel, nuser;
  cin >> nuser;
  cin >> nrel;
  nodes.resize(nuser);
  int tmp1, tmp2;
  for (int i = 0; i < nrel; i++) {
    cin >> tmp1 >> tmp2;
    nodes[tmp1].friends.push_back(tmp2);
    nodes[tmp2].friends.push_back(tmp1);
  }

  int q, s, t;
  cin >> q;
  for (int i = 0; i< q; i++) {
    cin >> s >> t;
    bfs(s);
    cout << (isAccessible(t) ? "yes" : "no") << endl;
  }
}

C++: #include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <vector>
#include <queue>
using namespace std;
const int INF=1<<21;
const int maxn=100+10;
int n,m,q;
int p[maxn];
int rank[maxn];
void init(int n)
{
   for(int i=0;i<n;i++)
   {
       p[i]=i;
       rank[i]=0;
   }
}
int fnd(int x)
{
    int y=x;
    if(x==p[x]) return x;
    while(x!=p[x])
    {
        x=p[x];
    }
    return p[y]=x;
}
bool is_same(int x,int y)
{
   return fnd(x)==fnd(y);
}

void uni(int x,int y)
{
   x=fnd(x);
   y=fnd(y);
   if(rank[x]>rank[y])
   {
       p[y]=x;
       rank[y]++;
   }
   else
   {
       p[x]=y;
       rank[x]++;
   }
}

int main()
{
//    freopen("in.txt","r",stdin);
    scanf("%d%d",&n,&m);
    int x,y;
    init(n);
    for(int i=0;i<m;i++)
    {
        scanf("%d%d",&x,&y);
        uni(x,y);
    }
    scanf("%d",&q);
    while(q--)
    {
        scanf("%d%d",&x,&y);
        if(is_same(x,y)) printf("yes\n");
        else printf("no\n");
    }


    return 0;
}

C++: #include<iostream>
#include<vector>
#include<stack>
using namespace std;
int i, j, v, num, color[100000];
vector<int> list[100000];

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(i=0; i<list[u].size(); i++){
     v = list[u][i];
     if(color[v] == -1){
       color[v] = c;
       S.push(v);
     }
   }
 }
}
 
void assigncolor(){
 int id = 1;
 for(i=0; i<num; i++){
   color[i] = -1;
 }
 for(i=0; i<num; i++){
   if(color[i] == -1)
     dfs(i, id++);
 }
}
 
int main(){
 int a, b, trial, start, goal, kaisuu;
 cin >> num >>kaisuu;
 
 for(i=0; i<kaisuu; i++){
   scanf_s("%d %d", &a, &b);
   list[a].push_back(b);
   list[b].push_back(a);
 }

 assigncolor();

 cin >> trial;

 for(i=1; i<=trial; i++){
   scanf_s("%d %d", &start, &goal);
   if(color[start] == color[goal]){  
     cout << "yes" << endl;
   } else{
     cout << "no" << endl;
   }
 }
 
 return 0;
}