Go: package main

import (
	"fmt"
	"bufio"
	"os"
	"strconv"
)

func main() {
	var n,m int
	fmt.Scan(&n)
	group := make([]int, n)
	for i := 0; i < n; i++ {
		group[i] = i
	}
	
	fmt.Scan(&m)
	sc := bufio.NewScanner(os.Stdin)
	sc.Split(bufio.ScanWords)
	for i := 0; i < m; i++ {
		sc.Scan()
		s, _ := strconv.Atoi(sc.Text())
		sc.Scan()
		t, _ := strconv.Atoi(sc.Text())

		if group[s] < group[t] {
			group[t] = group[s]
		} else {
			group[s] = group[t]
		}
	}

	sc.Scan()
	q, _ := strconv.Atoi(sc.Text())
	for i := 0; i < q; i++ {
		sc.Scan()
		s, _ := strconv.Atoi(sc.Text())
		sc.Scan()
		t, _ := strconv.Atoi(sc.Text())

		if root(s, &group) == root(t, &group) {
			fmt.Println("yes")
		} else {
			fmt.Println("no")
		}
	}
}

func root(i int, group *[]int) int {
	if i == (*group)[i] {
		return i
	}
	(*group)[i] = root((*group)[i], group)
	return (*group)[i]
}

C++: #include <iostream>

using namespace std;

const int N = 100000;
int A[N][N] = {{0}};
int n;

bool dfs(int s, int t) {
    if (A[s][t] == 1) {
        return true;
    }
    for (int i = 0; i < n; ++i) {
        if (i != t && A[s][i] != 0) {
            if (dfs(i, t)) {
                return true;
            }
        }
    }
    return false;
}

int main() {
    int m;
    cin >> n >> m;
    for (int i = 0; i < m; ++i) {
        int s, t;
        cin >> s >> t;
        A[s][t] = 1;
    }

    int q;
    cin >> q;
    for (int j = 0; j < q; ++j) {
        int x, y;
        cin >> x >> y;

        if (dfs(x, y)) {
            cout << "yes";
        } else {
            cout << "no";
        }
        cout << endl;
    }

    return 0;
}

C++: #include<iostream>
#include<vector>
#include<stack>
using namespace std;
static const int MAX = 100000;
static const int NTL = -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]==NTL){
      color[v]=c;
      S.push;
      }
    }
  }
}

void assigncolor() {
  int id=1;
  for(int i=0;i<n;i++) color[i]=NTL;
  for(int u =0;u<n;u++){
    if(color[u]==NTL)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);
  }

  assigncolor();

  cin >> q;

  for(int 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 <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) break;
    }
    if(find) cout<<"yes"<<endl;
    else cout<<"no"<<endl;
  }
  return 0;
}

C++: #include <iostream>
#include <string>
#include <vector>
using namespace std;
typedef long long ll;
const int INF = 1<<30; 
const int MOD = 1e9 + 7;
const int MAX_N = 100100;
template<typename Type> struct UnionFind
{
    vector<Type> p, r;
    UnionFind(int sz)
    {
        p.resize(sz);
        r.resize(sz, -1);
        for(int i = 0; i < sz; i++) p[i] = i;
    }
    Type Find(Type x)
    {
        if (x == p[x]) return x;
        return p[x] = Find(p[x]);
    }
    bool isSame(Type a, Type b) { return Find(a) == Find(b); }
    void unite(Type a, Type b)
    {
        a = Find(a), b = Find(b);
        if(a == b) return;
        if(r[a] < r[b]) p[a] = b;
        else { p[b] = a; if(r[a] == r[b]) r[a]++; }
    }
};
int main()
{
    cin.tie(0);
    ios::sync_with_stdio(false);
    int n, m; cin >> n >> m;
    UnionFind<int> UF(n + 1);
    for(int i = 0; i < m; i++)
    {
        int s, t; cin >> s >> t;
        if(UF.isSame(s, t)) continue;
        UF.unite(s, t);
    }
    int q; cin >> q;
    for(int i = 0; i < q; i++)
    {
        int s, t; cin >> s >> t;
        cout << (UF.isSame(s, t) ? "yes" : "no") << "\n";
    }
    return 0;
}

C++: #include<iostream>
#include<vector>
using namespace std;

int main(){
	int n,m,q,i,j;
	int s,t;
	vector<int> L(100005,-1);
	cin >> n >> m;
	
	for (j=0;j<n;j++){
		L[j]=j;
	}
	
	for (i=0;i<m;i++){
		cin >> s >> t ;
		if (L[s]!=L[t]){
			for (j=0;j<n;j++){
				if (L[j]==L[t]){
					L[j]=L[s];
				}
			}
		}
	}
	
	cin >> q;
	for (i=0;i<q;i++){
		cin >> s >> t;
		if (L[s]==L[t]){
			cout << "yes" <<endl;
		}else{
			cout << "no" <<endl;
		}
	}
	return 0;
}

C++: #include<bits/stdc++.h>
using namespace std;
static const int MAX=100000;
static const int NIL=-1;
int n;
vector<int>G[MAX]; //頂点数を100000とする
                   //隣接リスト
int color[MAX];
void dfs(int r,int c){
  stack<int>S;
  S.push(r); //始点rをスタックに追加
  color[r]=c;//色を入れる
  while(!S.empty()){ //スタックがからでない間
    int u=S.top();
    S.pop(); //スタックから頂点uを取り出し訪問
    for(int i=0;i<G[u].size();i++){
      //頂点uに隣接する頂点vを探索
      int v=G[u][i];
      if(color[v]==NIL){
	color[v]=c;
	S.push(v); //id(色)は変わらない
      }
    }
  }
}
int main(){
  int m,s,t,q;
  cin>>n>>m;
  for(int i=0;i<m;i++){
    cin>>s>>t;
    G[s].push_back(t); //sからtへ辺
    G[t].push_back(s); //tからsへ辺
  }
  int id=1; //colorに入れる色(情報)
  for(int i=0;i<n;i++){
    color[i]=NIL; //全てにNIL
  }
  for(int u=0;u<n;u++){
    if(color[u]==NIL) dfs(u,id++); //id(色)にかぶりがないように
  }
  cin>>q;
  for(int i=0;i<q;i++){
    cin>>s>>t;
    if(color[s]==color[t]){
      cout<<"yes"<<endl;
    }else{
      cout<<"no"<<endl;
    }
  }
  return(0);
}