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<stack>
using namespace std;

#define N 100000
#define WHITE 0  // 未訪問
#define BLACK 1  // 訪問ずみ

// 連結成分の番号を振る関数
void dfs(int n, int comp[], vector<int> G[]) {
  int i, j, vertex, neighbor, color[N];
  stack<int> S;
  // 初期状態
  for (i = 0; i < n; i++) color[i] = WHITE;

  for (i = 0; i < n; i++) {
    if (color[i] == WHITE) {
      // dfs
      S.push(i);
      while (!S.empty()) {
        vertex = S.top();
        S.pop();        
        color[vertex] = BLACK;  // 訪問済みにする
        comp[vertex] = i;  // 連結成分の番号を振る          
        for (j = 0; j < (int) G[vertex].size(); j++) {
          neighbor = G[vertex][j]; // 隣接している頂点：友人
          if (color[neighbor] == WHITE) S.push(neighbor);
        }
      }
    }
  }
}

int main() {
  int i, n, m, q, s, t;
  int comp[N];  // 連結成分の番号
  vector<int> G[N];  // グラフを表現する隣接リスト

  cin >> n >> m;
  // 隣接リストを作成
  for (i = 0; i < m; i++) {
    cin >> s >> t;
    G[s].push_back(t);
    G[t].push_back(s);
  }

  // グラフを連結成分に分ける
  dfs(n, comp, G);

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

C++: #include<iostream>
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define rep(i,n) for(int i=0;i<n;i++)
using P = pair<int,int>;

/* 大文字を小文字に変換 */
char tolower(char c) {return (c + 0x20);}
/* 小文字を大文字に変換 */
char toupr(char c) {return (c - 0x20);}

// if('A'<=s[i] && s[i]<='Z') s[i] += 'a'-'A';

/*
string s = "abcdefg"
s.substr(4) "efg"
s.substr(0,3) "abc"
s.substr(2,4) "cdef"

// イテレータ要素のインデックス
distance(A.begin(), itr);
*/

const int MAX_N = 100100;
const int NO = -1;
const int WHITE = 0, GRAY = 1, BLACK = 2;

int n, m;
vector<int> adl[MAX_N]; // 隣接リスト
int color[MAX_N], group[MAX_N];
queue<int> Q;

void init(){
    rep(i,MAX_N){
        color[i] = WHITE;
        group[i] = NO;
    }
}

void bfs(int u, int c){
    color[u] = GRAY;
    group[u] = c;
    Q.push(u);

    while(!Q.empty()){
        u = Q.front(); Q.pop();
        for(auto v: adl[u]){
            if(color[v] == WHITE){
                color[v] = GRAY;
                group[v] = c;
                Q.push(v);
            }
        }
        color[u] = BLACK;
    }
}

void bfs_visit(){
    rep(i,n){
        if(group[i] == NO) bfs(i, i);
    }
}

int main()
{
    cin >> n >> m;
    init();
    rep(i,m){
        int s, t; cin >> s >> t;
        adl[s].push_back(t);
        adl[t].push_back(s);
    }
    bfs_visit();
    int q; cin >> q;
    rep(_,q){
        int s, t; cin >> s >> t;
        if(group[s] == group[t]) cout << "yes" << endl;
        else cout << "no" << endl;
    }
    //rep(i,n) cout << group[i] << endl;
}

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

static const int INF=(1<<21);

int n,M[101][101];
int d[101];//最短距離を記録（到達不可能な時は、INf)

void bfs(int s){
  queue<int>q;
  q.push(s);//始点sを入れる（訪問）

  for(int i=0;i<n;i++) d[i]=INF;

  d[s]=0;
  while(!q.empty()){//空でない
    int u=q.front();//頂点を取り出す
    q.pop();
    for(int v=0;v<n;v++){
      if(M[u][v]==0) continue;//辺がない
      if(d[v]!=INF) continue; //訪問したことがある
      d[v]=d[u]+1;//vは未訪問の頂点　隣接しているためd[u]に1を足す
      q.push(v);//vを始点に
    }
  }
  for(int i=0;i<n;i++){
    cout<<i+1<<" "<<( (d[i]==INF) ? (-1):d[i] )<<endl;
  }
}

int main(){
  int u,k,v;

  cin>>n;

  for(int i=0;i<n;i++){
    cin>>u>>k;
    u--;
    for(int j=0;j<k;j++){
      cin>>v;
      v--;
      M[u][v]=1;
    }
  }

  bfs(0);

  return 0;
}

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

int main(void){cin.tie(0);ios::sync_with_stdio(false);
 
    //setup
    int nb_v; cin>>nb_v;
    int nb_e; cin>>nb_e;
    vector<int> union_tree( nb_v, -1 );
    for(int i=0; i<nb_e; ++i){
        int v1, v2; cin>>v1>>v2;
        if(v1>v2) swap(v1,v2);
        union_tree[v2] = v1;
    }
    
    //solve
    int times; cin>>times;
    for(int i=0; i<times; ++i){
        int from_v; cin>>from_v;
        int to_v; cin>>to_v;
        if (from_v<to_v) swap(from_v, to_v);
        
        int now_v = from_v;
        bool isPossible = false;
        while (now_v!=-1){
            if (union_tree[now_v] == to_v){
                isPossible = true;
                break;
            }
            now_v = union_tree[now_v];
        }
        cout<<(isPossible? "yes\n":"no\n");
    }    
}