Go: package main

import (
	"bufio"
	"container/list"
	"fmt"
	"os"
	"strconv"
)

//util
var sc = bufio.NewScanner(os.Stdin)

func nextStr() string {
	sc.Scan()
	return sc.Text()
}

func nextInt() int {
	sc.Scan()
	i, e := strconv.Atoi(sc.Text())
	if e != nil {
		panic(e)
	}
	return i
}

func printList(list []int) {
	n := len(list)
	buf := bufio.NewWriter(os.Stdout)
	for _, v := range list[0 : n-1] {
		buf.Write([]byte(fmt.Sprintf("%d ", v)))
	}
	buf.Write([]byte(fmt.Sprintf("%d\n", list[n-1])))
	buf.Flush()
}

func max(a, b int) int {
	if a > b {
		return a
	} else {
		return b
	}
}

func min(a, b int) int {
	if a > b {
		return b
	} else {
		return a
	}
}

//solve
const (
	MAX = 100000
	NIL = -1
)

var (
	n, m, q, s, t int
	G             [MAX][]int //連結リスト
	color         [MAX]int
)

func dfs(r int, c int) {
	S := list.New()
	S.PushFront(r)
	color[r] = c
	for S.Len() != 0 {
		u := S.Remove(S.Front()).(int)
		for i := 0; i < len(G[u]); i++ {
			v := G[u][i]
			if color[v] == NIL {
				color[v] = c
				S.PushFront(v)
			}
		}
	}
}

//幅優先探索で、頂点を色付け
func assignColor() {
	id := 1
	for i := 0; i < n; i++ {
		color[i] = NIL
	}
	for i := 0; i < n; i++ {
		if color[i] == NIL {
			id++
			dfs(i, id)
		}
	}
}

func main() {
	sc.Split(bufio.ScanWords)
	n, m = nextInt(), nextInt()
	for i := 0; i < m; i++ {
		s, t = nextInt(), nextInt()
		if i == 0 {
			G[s] = make([]int, 0)
			G[t] = make([]int, 0)
		}
		G[s] = append(G[s], t)
		G[t] = append(G[t], s)

	}
	assignColor()
	q = nextInt()
	for i := 0; i < q; i++ {
		s, t = nextInt(), nextInt()
		if color[s] == color[t] {
			fmt.Println("yes")
		} else {
			fmt.Println("no")
		}
	}

}

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;
}

C++: #include<iostream>
#include<queue>
#include<vector>
#include<cstring>
using namespace std;
queue<int>Q; int x[200000], n, m, q, s, t; vector<int>a[100000];

bool bfs(int A,int B) {
	memset(x, 0, sizeof(x));
	x[A] = 1;
	while (!Q.empty()) {
		for (int k = 0; k < a[Q.front()].size(); k++) {
			if (x[a[Q.front()][k]] == 0) { Q.push(a[Q.front()][k]); x[a[Q.front()][k]] = 1; }
		}
	}
	if (x[B] == 1) {
		return true;
	}
	else {
		return false;
	}
}

int main() {
	cin >> n >> m;
	for (int i = 0; i < m; i++) {
		cin >> s >> t;
		a[s].push_back(t);
		a[t].push_back(s);
	}
	cin >> q;
	for (int i = 0; i < q; i++) {
		cin >> s >> t;
		if (bfs(s, t)) { cout << "yes" << endl; }
		else { cout << "no" << endl; }
	}
	return 0;
}