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<iostream>


#include<queue>
using namespace std;
int main()
{
    int person_number,relation_number;

    cin>>person_number>>relation_number;

    vector<vector<int > > list(person_number);
    for(int i=0;i<relation_number;i++)
    {
        int start,end;
        cin>>start>>end;
        int flag=0;
        for(auto n:list[start])
        {
            if(n==end)
                flag=1;
        }
        if(flag==0) list[start].push_back(end);
        flag=0;
        for(auto n:list[end])
        {
            if(start==n) flag=1;
        }
        if(flag==0) list[end].push_back(start);
    }

    int test_number;
    cin>>test_number;
for(int i=0;i<test_number;i++)
{
    int from,to;
    cin>>from>>to;
    queue<int> q;
    q.push(from);
    vector<int> ban_list;
    for(int i=0;i<person_number;i++)
    {
        ban_list.push_back(0);
    }
    ban_list[from]=1;
    for(;!q.empty();q.pop())
    {
        int flag=0;
        for(auto n:list[q.front()])
        {
            if(n==to)  flag=1;
            if(ban_list[n]==0)
            {
                ban_list[n]=1;
                q.push(n);
            }
        }
        if(flag==1) break;
    }
    if(!q.empty()) cout<<"yes"<<endl;
    else cout<<"no"<<endl;
}
    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 j=0; j<G[u].size(); j++){
            int v = G[u][j];
            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 i=0; i<n; i++){
        if(color[i]==NIL)
            dfs(i, 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;
}

C++: #include<iostream>
#include<vector>
#include<stack>
#define rep(i, n) for (int i=0; i<(n); i++)
using namespace std;
static const int N=100000;
static const int NIL=-1;

int n,m,q;
vector<int> G[N];
int color[N];

void dfs(int r, int c) {
  stack<int> S;
  S.push(r);
  color[r]=c;
  while (!S.empty()) {
    int u=S.top();
    S.pop();
    rep(i, G[u].size()) {
      int v=G[u][i];
      if (color[v]==NIL) {
        color[v]=c;
        S.push(v);
      }
    }
  }
}

void assignColor() {
  int id=1;
  rep(i, n) color[i]=NIL;
  rep(u, n) {
    if (color[u]==NIL) dfs(u, id++);
  }
}

int main() { 
  cin>>n>>m;
  rep(i, m) {
    int s,t; cin>>s>>t;
    G[s].push_back(t);
    G[t].push_back(s);
  }
  assignColor();
  cin>>q;
  vector<int> X(q), Y(q);
  rep(i, q) cin>>X[i]>>Y[i];
  rep(i, q) {
    if (color[X[i]]==color[Y[i]]) cout<<"yes"<<endl;
    else cout<<"no"<<endl;
  }
  return 0;
}

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

int n, m, s, t, u;
vector<vector <int> > a;
int f[100000];

void path(int s1, int w) {
	f[s1] = w;
	for (int i = 0; i < (int) a[s1].size(); i++)
		if (f[a[s1][i]] == 0)
			path(a[s1][i], w);
	return;
}

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

	a.resize(n);

	for (int i = 0; i < m; i++) {
		int u, v;
		cin >> u >> v;
		a[u].push_back(v);
		a[v].push_back(u);
	}

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

	int j = 0, k = 1;
	while (j < n) {
		if (f[j] == 0) {
			path(j, k);
			k++;
		}
		j++;
	}

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

	if(f[s] == f[t])
		cout << "yes" << endl;
	else
		cout << "no" << endl;
	}

	return 0;
}

C++: #include <iostream>
#include <vector>
#define eol '\n'
using namespace std;

vector<int> group;

void bfs(int v, int g, vector< vector<int> > list) {
  if (group[v] != 0) {
    return;
  }
  group[v] = g;
  for (int i = 0; i < list[v].size(); i++) {
    bfs(list[v][i], g, list);
  }
}

int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);

  int n,m,s,t,q;
  cin >> n >> m;

  vector< vector<int> > list(n, vector<int>());
  group = vector<int>(n,0);
  
  for (int i = 0; i < m; i++) {
    cin >> s >> t;
    list[s].push_back(t);
    list[t].push_back(s);
  }

  int g = 1;
  for (int i = 0; i < n; i++) {
    if (group[i] == 0) {
      bfs(i, g, list);
      g++;
    }
  }

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