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 <algorithm>
#include <vector>
#include <queue>
using namespace std;
int a[100000],gp[1000000],g=0;
int inf=100000,n,m;
vector< vector<int> > v(100000);
void dfs(int s){
    gp[s]=g;
    a[s]=inf;
    for(int i=0;i<(int)v[s].size();i++){
        if(a[v[s][i]]!=inf){
            dfs(v[s][i]);
        }
    }
}
int main(){
  cin>>n>>m;
  for(int i=0;i<m;i++){
      int tmp,u;
      cin>>tmp>>u;
      v[tmp].push_back(u);
      v[u].push_back(tmp);
  }
  dfs(0);
  for(int i=0;i<n;i++){
      g++;
      if(!a[i])dfs(i);
  }
  int qu;
  cin>>qu;
  int s[qu],t[qu];
  for(int i=0;i<qu;i++)cin>>s[i]>>t[i];
  for(int i=0;i<qu;i++){
      if(gp[s[i]]==gp[t[i]])
          cout<<"yes\n";
      else
          cout<<"no\n";
  }
}

C++: // ALDS1_11_D.cpp
// Graph I - Connected Components

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

bool isFriend(vector<vector<int>> &sns, vector<int> &arrived, int x, int y)
{
    for (int i = 0; i < sns[x].size(); i++) {
        if (sns[x][i] == y) return true;
    }

    bool res = false;
    arrived[x] = 1;
    for (int i = 0; i < sns[x].size(); i++) {
        if (!arrived[i]) {
            bool tmp = isFriend(sns, arrived, i, y);
            if (tmp) {
                res = true;
                break;
            }
        }
    }
    return res;
}

int main()
{
//    freopen("ALDS1_11_D_in20.txt", "r", stdin);
//    freopen("out20.txt", "w", stdout);
    int m, n, q;
    cin >> n >> m;
    vector<vector<int> > sns(n, vector<int>());
    int x, y;
    for (int i = 0; i < m; i++) {
        cin >> x >> y;
        sns[x].push_back(y);
        sns[y].push_back(x);
    }

    cin >> q;
    while (q--) {
        vector<int> arrived(n);
        cin >> x >> y;
        bool res = isFriend(sns, arrived, x, y);
        if (res) cout << "yes" << endl;
        else cout << "no" << endl;
    }
    return 0;
}

C++: #include <iostream>
#include <algorithm>
#include <vector>
#include <deque>
#include <queue>
#include <list>
#include <stack>
#include <string>
#include <tuple>
#include <functional>
#include <numeric>
#include <cmath>
#include <iomanip>
#include <map>
#include <random>
#include <cstdlib>
#define Loop(i, n) for(int i = 0; i < (int)n; i++)
#define Loop1(i, n) for(int i = 1; i <= (int)n; i++)
#define Loopr(i, n) for(int i = (int)n - 1; i >= 0; i--)
#define Loopr1(i, n) for(int i = (int)n; i >= 1; i--)
using namespace std;
typedef long long int ll;

static const int N = 100005;
vector<int> V[N], visit(N, 0), color(N, 0);
queue<int> Q;

void paint(int c) {
	while (Q.size() > 0) {
		int u = Q.front();
		Q.pop();
		color[u] = c;
		Loop(i, V[u].size()) {
			if (color[V[u][i]] == 0) {
				Q.push(V[u][i]);
			}
		}
	}
}

int main() {
	int n, m;
	cin >> n >> m;
	Loop(i, m) {
		int s, t;
		cin >> s >> t;
		V[s].push_back(t);
		V[t].push_back(s);
	}
	//color painting
	int c = 0;
	Loop(i, n) {
		if (color[i] == 0) {
			c++;
			Q.push(i);
			paint(c);
		}
	}
	//end
	int q;
	cin >> q;
	Loop(i, q) {
		int s, t;
		cin >> s >> t;
		if (color[s] == color[t]) cout << "yes" << endl;
		else cout << "no" << endl;
	}
}

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

int n;
int **connection;

bool isFriend(int s, int t){
    int i;
    int f[n];
    for(i=0;i<n;i++)f[i]=0;
    f[s]=1;
    int u;
    queue<int> q;
    q.push(s);
    while(!q.empty()){
        u=q.front();q.pop();
        for(i=0;i<n;i++){
            if(connection[u][i]&&f[i]==0){
                connection[u][i]=1;
                connection[i][u]=1;
                if(i==t)return true;
                f[i]=1;
                q.push(i);
            }
        }
    }
    return false;
}

int main(){
    int i, j, m, s, t, q;
    scanf("%d %d",&n,&m);
    connection = (int **)malloc(sizeof(int *)*n);
    for(i=0;i<n;i++){
        connection[i] = (int *)malloc(sizeof(int)*n);
        for(j=0;j<n;j++){
            connection[i][j]=0;
        }
    }
    for(i=0;i<m;i++){
        scanf("%d %d",&s,&t);
        connection[s][t]=1;
        connection[t][s]=1;
    }
    scanf("%d",&q);
    for(i=0;i<q;i++){
        scanf("%d %d",&s,&t);
        if(isFriend(s,t))printf("yes\n");
        else printf("no\n");
    }
    return 0;
}

C++: #include<cstdio>
#include<vector>
#include<algorithm>
#include<utility>
#include<numeric>
#include<iostream>
#include<array>
#include<string>
#include<sstream>
#include<stack>
#include<queue>
#include<list>
#define _USE_MATH_DEFINES

#include<math.h>
#include<map>

#define SENTINEL 1000000001

#define min(a,b) (a)>(b)?(b):(a)
#define max(a,b) (a)>(b)?(a):(b)

using namespace std;

int from[100000];
int to[100000];

bool checked[100000];

bool judge(int f, int t,int n)
{
	if (checked[f])
	{
		return false;
	}

	checked[f] = true;

	bool isFriend = false;
	for (int i = 0; i < n; i++)
	{
		if (from[i] == f)
		{
			if (to[i] == t)
			{
				isFriend = true;
			}
			else
			{
				isFriend = judge(to[i], t, n);
			}
			if (isFriend)
			{
				break;
			}
		}
		if (to[i] == f)
		{
			if (from[i] == t)
			{
				isFriend = true;
			}
			else
			{
				isFriend = judge(from[i], t, n);
			}
			if(isFriend)
			{
				break;
			}
		}
	}
	return isFriend;
}

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

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

		from[i] = f;
		to[i] = t;
	}

	int q;
	cin >> q;

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

		for (int i = 0; i < n; i++)
		{
			checked[i] = false;
		}

		printf(judge(f, t, n) ? "yes\n" : "no\n");
	}
	return 0;
}