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>
#include <vector>

std::vector<int> v[100010];
int n;
int m;

bool visited[10010];

/**
bool dfs(int from, int to) {

  if(visited[to]) {
    return true;
  }

  visited[from] = true;
  for(int u=0; u<v[from].size(); ++u) {
    if(visited[v[from][u]]) continue;
    else {
      visited[v[from][u]] = true;
      dfs(v[from][u], to);
    }
  }

  return false;
}
**/

void dfs(int from) {
  visited[from] = true;
  for(int u=0; u<v[from].size(); ++u) {
    if(visited[v[from][u]]) continue;
    else {
      dfs(v[from][u]);
    }
  }
}

int main() {
  std::cin >> n >> m;

  for(int i=0; i<m; ++i) {
    int from, to;
    std::cin >> from >> to;
    v[from].push_back(to);
    v[to].push_back(from);
  }

  int q_n;
  std::cin >> q_n;
  bool answers[10010];
  for(int i=0; i<q_n; ++i) {
    int from, to;
    std::cin >> from >> to;
    for(int j=0; j<n; ++j) visited[j] = false;

    dfs(from);
    answers[i] = visited[to];
  }

  for(int i=0; i<q_n; ++i) {
    if(answers[i]) std::cout << "yes" << std::endl;
    else std::cout << "no" << std::endl;
  }

}

C++: #include <bits/stdc++.h>
using namespace std;
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define rep(i,n)   for(int i=0;i<(n);++i)
#define SORT(c)    sort((c).begin(),(c).end())
#define CLR(a)     memset((&a), 0 ,sizeof(a))//clear memory
#define dump(x)    cerr << #x << " = " << (x) << endl;//debug
#define debug(x)   cerr << #x << " = " << (x) << " (L" << __LINE__ << ")" << " " << __FILE__ << endl;
#define EPS        1e-10//sample:if((double)>=(double)+EPS)
//cin,cout release
//std::cin.tie(0);
//ios::sync_with_stdio(false);

using namespace std;

vector<int> G[200001];
int color[200001];
int s[10000],head,tail;
void dfs(int r,int c){
  head=tail=0;
  s[tail++]=r;
  color[r]=c;
  while(head!=tail){
    int u=s[head++];
    for(int i=0;i<(int)G[u].size();i++){
      int v=G[u][i];
      // if(v!=0){
	if(color[v]==-1){
	  s[tail++]=v;
	  color[v]=c;
	}
	//}
    }
  }
}
int main(){
  int n,m,ia,ib,p,id=1;
  rep(i,200000)color[i]=-1;
  cin>>n>>p;
  rep(i,p){
    cin>>ia>>ib;
    G[ia].push_back(ib);
  }
  rep(i,p)if(color[i]==-1)dfs(i,id++);
  cin>>m;
  rep(i,m){
    cin>>ia>>ib;
    if(color[ia]==color[ib])cout<<"yes"<<endl;
    else cout<<"no"<<endl;
  }

  return 0;
}

C++: /* 
 * ALDS1_11B.cpp
 */
#include <iostream>
#include <queue>
#include <cstdio>
#include <cstdlib>
#include <cstring>

using namespace std;

using Friends = vector<int>;
using SNS = vector<Friends>;

int n, m, q;
bool visited[100000];
SNS sns;

bool is_friend(int id, int target) {
    if (visited[id])
        return false;

    visited[id] = true;
    for (int i = 0; i < sns[id].size(); ++i) {
        int now = sns[id][i];
        if (is_friend(now, target))
            return true;
    }
    return false;
}

int main(void) {

    scanf("%d %d", &n, &m);
    sns.resize(n);
    for (int i = 0, id, f; i < m; ++i) {
        scanf("%d %d", &id, &f);
        sns[id].push_back(f);
        sns[f].push_back(id);
    }

    scanf("%d", &q);
    for (int i = 0, id, f; i < q; ++i) {
        scanf("%d %d", &id, &f);
        memset(visited, 0, sizeof(bool) * n);
        if (is_friend(id, f))
            printf("yes\n");
        else
            printf("no\n");
    }

    return 0;
}

C++: #include <iostream>
#include <assert.h>
using namespace std;
#define MAX_V 100000

int represent[MAX_V];
int status[MAX_V];

int findRepresent(int x)
{
    if (represent[x] == x) {
        return x;
    } else {
        represent[x] = findRepresent(represent[x]);
        return represent[x];
    }
}

void unite(int x, int y)
{
    x = findRepresent(x);
    y = findRepresent(y);
    if (x == y)
        return;
    if (status[x] < status[y])
        swap(x, y);
    assert(status[x] >= status[y]);
    represent[y] = x;
    if (status[x] == status[y])
        status[x]++;
}

bool same(int x, int y)
{
    return (findRepresent(x) == findRepresent(y));
}

int main()
{
    for (int i = 0; i < MAX_V; ++i) {
        represent[i] = i;
        status[i] = 0;
    }

    int n, m;
    cin >> n >> m;
    for (int i = 0; i < m; ++i) {
        int a, b;
        cin >> a >> b;
        unite(a, b);
    }
    for (int i = 0; i < n; ++i) {
        cout << represent[i] << " " << status[i] << endl;
    }
    int q;
    cin >> q;
    for (int i = 0; i < q; ++i) {
        int from, to;
        cin >> from >> to;
        cout << (same(from, to)? "yes" : "no") << '\n';
    }
    return 0;
}

C++: //16D8103013E Sen Shunkou
#include<iostream>
#include<queue>
int main(){
    //input
    int n,m;
    std::cin>>n;
    std::cin>>m;
    int A[n][n];
    bool visited[n];
    int judge[n];

    for(int i=0;i<n;i++){
        judge[i]=-1;
        visited[i]=false;
        A[i][0]=0;
        for(int j=1;j<n;j++){
            A[i][0]=0;
            A[i][j]=-1;
        }    
    }

    int cnt_i=0,cnt_j=0;
    for(int k=0;k<m;k++){
        int i,j;
        std::cin>>i;
        std::cin>>j;
        A[i][0]++; cnt_i=A[i][0];
        A[j][0]++; cnt_j=A[j][0];
        A[i][cnt_i]=j;
        A[j][cnt_j]=i;
    }

    /*for(int i=0;i<10;i++){
        for(int j=0;j<10;j++){
            std::cout<<" "<<A[i][j];
        }
        std::cout<<std::endl;
    }*/

    int n_2;
    std::cin>>n_2;
    for(int i=0;i<n_2;i++){
        int s,e;
        std::cin>>s;
        std::cin>>e;
        
        int cnt=0;
        for(int i=0;i<n;i++){
            judge[i]=-1;
            visited[i]=false;
        }
        
        std::queue<int> que;
        que.push(s);
        /*for(int i=0;i<10;i++){
            for(int j=0;j<10;j++){
                //std::cout<<" "<<A[i][j];
            }
            //std::cout<<std::endl;
        }*/
        while(!que.empty()){
            int q=que.size();
            for(int k=0;k<q;k++){
                //std::cout<<"quesize"<<que.size()<<"\n";
                int i=que.front();
                que.pop();
                visited[i]=true;
                judge[i]=cnt;
                //std::cout<<i<<"cnt"<<cnt<<"\n";
                //std::cout<<A[i][0]<<"\n";
                if(A[i][0]!=0){
                    for(int j=0;j<A[i][0];j++){
                        if(visited[A[i][j+1]]!=true){
                            visited[A[i][j+1]]=true;
                            que.push(A[i][j+1]);
                        }
                    }
                }
            }
            cnt++;
        }
        if(judge[e]==-1){
            std::cout<<"no\n";
        }else std::cout<<"yes\n";
    }

    return 0;
}