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 <cstdio>
#include <climits>
#include <cmath>
#include <algorithm>
#include <utility>
#include <vector>
#include <string>
#include <stack>
#include <queue>
#define MAX 100000
#define INFTY 1<<30 // 2^30
using namespace std;
typedef long long llong;
 
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 assingColor()
{
  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);
  }
 
  assingColor();
 
  cin >> q;
  for(int i = 0; i < q; i++)
  {
    cin >> s >> t;
    cout << ((color[s] == color[t]) ? "yes" : "no") << endl;
  }
  return 0;
}

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

using namespace std;

int n, color[10000];
vector<int> G[10000];

void dfs (int r, int c) {

    int i, u, v;

    stack<int> S;
    S.push(r);
    color[r] = c;

    while (!S.empty()) {
        u = S.top();
        S.pop();
        for (i = 0; i < G[u].size(); i++) {
            v = G[u][i];
            if (color[v] == -1) {
                color[v] = c;
                S.push(v);
            }
        }
    }

}

void assignColor () {

    int id = 1, i, u;

    for (i = 0; i < n; i++) {
        color[i] = -1;
    }
    for (u = 0; u , n; u++) {
        if (color[u] = -1) {
            dfs (u, id++);
        }
    }

}

int main () { 

    int s, t, m, q, i;

    cin >> n >> m;

    for (i = 0; i < m; i++) {
        cin >> s >> t;
        G[s].push_back(t);
        G[t].push_back(s);
    }

    assignColor ();

    cin >> q;

    for (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<stdio.h>
#include<vector>
#include<queue>
#define MAX 100000
using namespace std;
int d[MAX];

int n;
vector <int> M[MAX];


int tail;



void BFS(int s,int t) {
	queue <int>Q;
	Q.push(s);
	d[s] = t;
	while (!Q.empty()) {
		s = Q.front();
		Q.pop();
		for (int j = 0; j < M[s].size(); j++) {
				
				if (d[M[s][j]] == -1) {
					d[M[s][j]] = t;
					Q.push(M[s][j]);
				}
		}

	}
}


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

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

	for (int i = 0; i < n; i++) {
		d[i] = -1;
	}
	int count = 0;
	for (int i = 0; i < n; i++) {
		if (d[i] == -1) {
			count++;
			BFS(i, count);
		}
	}
	cin >>q;
	for (int i = 0; i < q; i++) {
		int s2, t2;
		scanf("%d %d", &s2, &t2);
		if (d[s2] == d[t2]) {
			printf("yes\n");
		}
		else {
			printf("no\n");
		}
		
		
	}
	
	return 0;
}

C++: #include<iostream>
#include<vector>
using namespace std;
void numbering(int v, int k, vector<vector<int>>const&graph, vector<int>&id) {
	
	id[v] = k;
	//v????????????????????????
	//id??????????????°?????????????????????
	//k????????????????????????
	for (auto to : graph[v]) {
		//for(int i=0;i<graph[v].size();++i)
		
		if (id[to] != -1) {
			continue;
		}
		numbering(to, k, graph, id);
	}
}
int main() {
	int n, m;
	cin >> n >> m;
	vector<vector<int>>graph(n);
	for (int i = 0;i < m;++i) {
		int u, v;
		cin >> u >> v;
		graph[u].push_back(v);
		graph[v].push_back(u);
	}
	vector<int>id(n, -1);
	for (int i = 0;i < n;i++) {
		if (id[i] == -1) {
			numbering(i, i, graph, id);
			//numbering(?????????????????????,?????????????????????,graph,id)
		}
	}
	int q;
	cin >> q;
	while (q--) {
		int u, v;
		cin >> u >> v;
		if (id[u] == id[v]) {
			cout <<"yes" << endl;
		}
		else {
			cout << "no" << endl;
		}
	}

}

C++: #include <stdio.h>

int m[100000] = {0};

void init() {
	int i;
	for ( i = 0; i < 100000; ++i) {
		m[i] = i;
	}
}

int find(int n) {
	if ( n == m[n]) {
		return n;
	}
	return m[n] = find(m[n]);
}

int friend (int x, int y) {
	if ( find(x) == find(y)) {
		return 1;
	} else {
		return 0;
	}
}

void unit (int x, int y) {
	x = find(x);
	y = find(y);
	
	if ( x == y ) {
		return ;
	}
	m[y] = x;
}

int main() {
	int n, s, t, u, v, i;
	init();
	scanf("%d", &n);
	scanf("%d", &s);
	
	for ( i = 0; i < s; ++i) {
		scanf("%d", &u);
		scanf("%d", &v);
		unit( u, v);
	}
	
	scanf("%d", &t);
	
	for ( i = 0; i < s; i++) {
		scanf("%d", &u);
		scanf("%d", &v);
		if ( friend( u, v) == 1) {
			printf("yes\n");
		} else {
			printf("no\n");
		}
	}
	return 0;
}

C++: #include <iostream>
#include <cstdio>
#define MAX 100000

using namespace std;

int main(){
  int a[MAX]={};
  int n,m; cin>>n>>m;
  int s,t;
  int group=1;
  for(int i=0;i<m;i++){
    cin>>s>>t;
    if(a[s]==0 && a[t]==0){
      a[s]=a[t]=group;
      group++;
    }else if(a[s]==0){
      a[s]=a[t];
    }else if(a[t]==0){
      a[t]=a[s];
    }else{
      int tmp=a[t];
      a[t]=a[s];
      for(int j=0;j<i;j++){
        if(a[j]==tmp) a[j]=a[s];
      }
    }
  }

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

}