Go: package main

import (
	"fmt"
)

var n, m int
var g [][]int
var color []int

func main() {
	fmt.Scan(&n, &m)
	g = make([][]int, n) // SNSの関係を表すグラフ
	for i := 0; i < m; i++ {
		var a, b int
		fmt.Scan(&a, &b)
		g[a] = append(g[a], b) // 無向重みなしグラフ
		g[b] = append(g[b], a)
	}
	color = make([]int, n) // 各ノードにつける色
	for i := 0; i < len(color); i++ {
		color[i] = -1 // 初期化しておく
	}
	type query struct {
		s, t int
	}
	var Q int
	fmt.Scan(&Q)
	qs := make([]query, Q)
	for i := 0; i < Q; i++ {
		fmt.Scan(&qs[i].s, &qs[i].t)
	}
	// fmt.Println("n", n, "m", m, "g", g, "Q", Q, "qs", qs)
	// 全ての頂点からdfsする
	id := 1
	for u := 0; u < n; u++ {
		if color[u] == -1 {
			dfs(u, id)
			id++
		}
	}
	// fmt.Println("color", color)
	for i := 0; i < Q; i++ {
		if color[qs[i].s] == color[qs[i].t] {
			fmt.Println("yes")
		} else {
			fmt.Println("no")
		}
	}
}

func dfs(v, c int) {
	// fmt.Printf("dfs(v %d, c %d) en:\n", v, c)
	color[v] = c
	for _, vv := range g[v] {
		// fmt.Printf("  v %d, g[v] %v, vv %d\n", v, g[v], vv)
		if color[vv] == -1 {
			dfs(vv, c)
		}
	}
}

C++: #include <bits/stdc++.h>
using namespace std;
int flag[100000];
vector<int> G[100000];
int color = 0;

void dfs(int f)
{
    for (int i = 0; i < G[f].size(); i++)
    {
        if (flag[G[f][i]] == -1)
        {
            flag[G[f][i]] = color;
            dfs(G[f][i]);
        }
    }
}

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

        cin >> f >> g;
        G[f].push_back(g);
        G[g].push_back(f);
    }

    for (int i = 0; i < n; i++)
        flag[i] = -1;

    for (int i = 0; i < n; i++)
    {
        if (flag[i] == -1)
        {
            color = i;
            flag[i] = color;
            dfs(i);
        }
    }
    int q;
    cin >> q;
    while (q--)
    {
        cin >> f >> g;
        if (flag[f] == flag[g])
            cout << "yes" << endl;
        else
            cout << "no" << endl;
    }
}

C++: #include<iostream>
#include<list>
#define MAX 100000
using namespace std;

class person
{
public:
	bool Isdone = false;
	list <person*> lis;
	bool serch(person* Per)
	{
		Isdone = true;
		while (!lis.empty())
		{
			person* temp = lis.front();
			lis.pop_front();
			if (temp == Per)return true;
			else if (temp->Isdone == true)continue;
			else
			{
				if (temp->serch(Per))return true;
			}
		}
		return false;
	}
};

int main()
{
	person *P;
	P = new person[MAX + 1];
	int n, m;
	cin >> n >> m;
	for (int i = 0; i < m; i++)
	{
		int p1, p2;
		cin >> p1 >> p2;
		P[p1].lis.push_back(&P[p2]);
		P[p2].lis.push_back(&P[p1]);
	}
	int q;
	cin >> q;
	for (int i = 0; i < q; i++)
	{
		int p1, p2;
		cin >> p1 >> p2;
		if (P[p1].serch(&P[p2]))
		{
			cout << "yes" << endl;
		}
		else
		{
			cout << "no" << endl;
		}
		for (int l = 0; l < n; l++)P[l].Isdone = false;
	}
	delete[] P;
	return 0;
}

C++: #include<iostream>
#include<vector>
#include<stack>
using namespace std;
int n,m;
static const int MAX = 100000;
static const int NIL = -1; 
vector<int> graph[MAX];
int color[MAX];
void dfs(int s,int t)
{
	
	stack<int> ss;
	ss.push(s);
	color[s]=t;
	while(!ss.empty())
	{
		int u=ss.top();
		ss.pop();
		for(int i=0;i<graph[u].size();i++)
		{
			int v=graph[u][i];
			if(color[v]==NIL)
			{
				color[v]=t;
				ss.push(v);
			}
		}
	}
}
void assigncolor()
{
	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()
{
	cin>>n>>m;
	
	for(int i=0;i<m;i++)
	{
		int s,t;
		cin>>s>>t;
		graph[s].push_back(t);
		graph[t].push_back(s);
	}
	assigncolor();
	int q;
	cin>>q;
	while(q--)
	{
		int s,t;
		cin>>s>>t;
		if(color[s]==color[t])
			cout<<"yes"<<endl;
		else cout<<"no"<<endl;
	}
	return 0;
 }

C++: #include <stdio.h>
#include <stack>
#include <iostream>
using namespace std;
int G[100000][100000];
int vis[100000];
int n;

bool dfs(int s, int t)
{
    if (G[s][t] == 1 || G[t][s] == 1) return true;
    vis[s] = 1;
    for (int i = 0; i < n; i++)
    {
        if (G[s][i] == 1 && vis[i] == 0)
            {
                bool a = (dfs(i,t)); 
                if(a) 
                {
                    vis[s] = 0;
                    return a;
                }
            }

    } 
    vis[s] = 0;
    return false;
}

int main()
{
    //freopen("in3.txt","r",stdin);
    int m;
    scanf("%d %d",&n, &m);
    for (int i = 0; i < n; i++)
    {
        vis[i] = 0; 
    } 
    for (int i = 0; i < n; i++)
    {
        for (int j = 0; j < n; j++)
        {
            G[i][j] = 0; 
        }  
    } 
    for (int i = 0; i < m; i++)
    {
        int s, t;
        scanf("%d %d",&s,&t); 
        G[s][t] = 1;
        G[t][s] = 1;
    } 
    int q,s,t;
    scanf("%d",&q);
    for (int i = 0; i < q; i++)
    {
        scanf("%d %d",&s,&t);
        if(dfs(s,t)||dfs(t,s)) printf("yes\n");
        else printf("no\n");
    } 
    return 0;
}

C++: #include<stdio.h>
#include<vector>
#include<string>
#include<iostream>
using namespace std;

vector<vector<int> >g;
int n,m,q,s,t;

vector<bool>visited;
vector<int>color;
void dfs(int s){
    for(int i=0;i<g[s].size();i++){
        if(color[g[s][i]]==-1){
            color[g[s][i]]=color[s];
            dfs(g[s][i]);
        }
    }
}
bool dfs2(int s,int t){
    if(s==t)return true;
    visited[s]=true;
    for(int i=0;i<g[s].size();i++){
        if(!visited[g[s][i]]){
            if(dfs2(g[s][i],t)){
                return true;
            }
        }
    }
    return false;
}
int main() {
    scanf("%d %d",&n,&m);
    g.resize(n);
    color.resize(n,-1);
    for(int i=0;i<m;i++){
        scanf("%d %d",&s,&t);
        g[s].push_back(t);
        g[t].push_back(s);
    }
    for(int i=0;i<n;i++){
        if(color[i]==-1){
            color[i]=i;
            dfs(i);
        }
    }
    scanf("%d",&q);
    visited.resize(n);
    for(int i=0;i<q;i++){
        scanf("%d %d",&s,&t);
        for(int j=0;j<n;j++)visited[j]=false;
        string s1=(dfs2(s,t)?"yes":"no");
        string s2=(color[s]==color[t]?"yes":"no");
        //if(s1!=s2&&s1=="yes")return 1;
        cout<<s1<<endl;
    }
    return 0;
}

C++: #include <iostream>
#include <map>
#include <queue>
using namespace std;
int main(){
  int n,m,t1,t2,c[100000]={}; map <int,bool> g[100000];
  cin>>n>>m;
  for(int i=0;i<m;i++){
    cin>>t1>>t2;g[t1][t2]=1;g[t2][t1]=1;
  }
  int l;cin>>l;
  for(int i=0;i<l;i++){
    queue <int> q;
    bool f[100000]={},find=false;
    cin>>t1>>t2;
    if(c[t1]&&c[t2]){
      if(c[t1]==c[t2]) cout<<"yes"<<endl;
      else cout<<"no"<<endl;
      continue;
    }
    q.push(t1);f[t1]=true;c[t1]=i+1;
    for(;!q.empty();){
      for(int j=0;j<n;j++) if(g[q.front()][j]&&!f[j]){
          if(j==t2) find=true;
          f[j]=true;c[t2]=i+1;
          q.push(j);
	}
      q.pop();
    }
    if(find) cout<<"yes"<<endl;
    else cout<<"no"<<endl;
  }
  return 0;
}

C++: #include<iostream>
#include<queue>
#include<vector>
using namespace std;
#define MAX_N 500000
vector<int>X[MAX_N]; queue<int>Q;
int COLOR[MAX_N], N, M, Q1, A, B;
int main() {
    cin >> N >> M;
    for (int i = 0; i < M; i++) { cin >> A >> B; X[A].push_back(B); X[B].push_back(A); }
    int cnt = 0;
    for (int i = 0; i < N; i++) {
        if (COLOR[i] == 0) {
            Q.push(i); cnt++; COLOR[i] = cnt;
            while (!Q.empty()) {
                int a = Q.front(); Q.pop();
                for (int j = 0; j < X[a].size(); j++) {
                    int to = X[a][j];
                    if (COLOR[to] == 0) {
                        COLOR[to] = cnt;
                        Q.push(to);
                    }
                }
            }
        }
    }
    cin >> Q1;
    for (int i = 0; i < Q1; i++) {
        cin >> A >> B;
        if (COLOR[A] == COLOR[B]) {
            cout << "yes" << endl;
        }
        else {
            cout << "no" << endl;
        }
    }
    return 0;
}