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 <iostream>
#include <vector>
#include <algorithm>
#include <queue>
#include <stack>
#include <stdio.h>
#include <cmath>
#include <set>
#include <map>
using namespace std;

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

vector<bool>visited;
bool dfs(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(dfs(g[s][i],t)){
                return true;
            }
        }
    }
    return false;
}
int main() {
    while(1){}
    cin>>n>>m;
    g.resize(n);
    
    for(int i=0;i<m;i++){
        int s,t;
        cin>>s>>t;
        g[s].push_back(t);
        g[t].push_back(s);
    }
    cin>>q;
    for(int i=0;i<q;i++){
        visited.resize(n,false);
        int s,t;
        cin>>s>>t;
        cout<<(dfs(s,t)?"yes":"no")<<endl;
    }
    return 0;
}

C++: #include<bits/stdc++.h>

using namespace std;

vector<int> numbers;

void setNum(vector<vector<int> > a){
    numbers.resize(a.size());
    for(int i = 0; i < numbers.size(); i++)numbers[i] = -1;
    int num = 0;
    queue<int> place;
    place.push(0);
    while(place.size()){
        int now = place.front();
        place.pop();
        numbers[now] = num;
        for(int i = 0; i < a[now].size(); i++){
            int next = a[now][i];
            if(numbers[next] == -1){
                place.push(next);
            }
        }
        if(place.size() == 0){
            for(int i = 0; i < numbers.size(); i++){
                if(numbers[i] == -1){
                    place.push(i);
                    num++;
                    break;
                }
            }
        }
    }
}

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

C++: #include<bits/stdc++.h>
using namespace std;
static const int MAX=100000;
static const int NIL=-1;
int n;
vector<int>G[MAX];//隣接リスト
int color[MAX];
void dfs(int r,int c){
  stack<int>S;
  S.push(r);
  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);
      }
    }
  }
}
int main(){
  int s,t,m,p;
  cin>>n>>m;
  for(int i=0;i<m;i++){
    cin>>s>>t;
    G[s].push_back(t);
    G[t].push_back(s);
  }
  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++);
    }
  }
  cin>>p;
  for(int i=0;i<p;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>

using namespace std;
struct user {
    user() {};
    user(int i) : id {i}, fs {}, group {-1} {};
    int id;
    vector<int> fs;
    int group;
};

void add_friends(user *us, int x, int y){
    us[x].fs.push_back(y);
    us[y].fs.push_back(x);
}

void dfs(user* us, int id, int g){
    stack<int> ss {};
    ss.push(id);
    while(ss.size()){
        int p = ss.top();
        ss.pop();
        us[p].group = g;
        vector<int> fs = us[p].fs;
        for(auto x : fs){
            if(us[x].group == g){
                continue;
            }
            ss.push(x);
        }
    }
}

void make_group(user* us, int n){
    int g = 0;
    for(int i = 0; i < n; ++i){
        if(us[i].group < 0){
            dfs(us, i, g);
            ++g;
        }
    }
}

int main(){
    int n, m;
    cin >> n >> m;
    user us[n];
    for(int i = 0; i < n; ++i){
        us[i] = user(i);
    }
    for(int i = 0; i < m; ++i){
        int a, b;
        cin >> a >> b;
        add_friends(us, a, b);
    }
    make_group(us, n);
    int q;
    cin >> q;
    for(int i = 0; i < q; ++ i){
        int a, b;
        cin >> a >> b;
        if(us[a].group == us[b].group){
            cout << "yes" << endl;
        } else {
            cout << "no" << endl;
        }
    }
}

C++: #include<bits/stdc++.h>
using namespace std;
#define rp(i,j) for(long long i=0;i<j;i++)
#define rep(i,j,k) for(long long i=j;i<k;i++)
#define mod 1000000007
#define NIL -1
#define MAX 100000
typedef long long ll;
int n;
vector<int>a[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();
        rp(i,a[u].size()){
            int v=a[u][i];
            if(color[v]==NIL){
                color[v]=c;
                S.push(v);
            }
        }
    }
}
void colordefine(){
    int id=1;
    rp(i,n)color[i]=NIL;
    rp(i,n){
        if(color[i]==NIL)dfs(i,id++);
    }
}
int main(){
    int m,s,t,q;
    cin>>n>>m;
    rp(i,m){
        cin>>s>>t;
        a[s].push_back(t);
        a[t].push_back(s);
    }
    colordefine();
    cin>>q;
    rp(i,q){
        cin>>s>>t;
        string ans;
        if(color[s]==color[t])ans="yes";
        else ans="no";
        cout<<ans<<endl;
    }
}

C++: #include <bits/stdc++.h>
using namespace std;
typedef long long ll;

const int NIL=-1;

int n, color[10000];
vector<int> G[100000];


void dfs(int v, int id){
    color[v]=id;

    for(int i=0; i<G[v].size(); i++){
        if(color[G[v][i]]==NIL) dfs(G[v][i],id);
    }
}

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); id++;
        }
    }
}

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

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

    assignColor();

    int q; cin >> q;
    for(int i=0; i<q; i++){
        int s,t; cin >> s >> t;
        if(color[s]==color[t]) printf("yes\n");
        else printf("no\n");
    }
}