Go: package main

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

func main() {
	sc := bufio.NewScanner(os.Stdin)
	sc.Split(bufio.ScanWords)

	nNodes := scanInt(sc)
	nConns := scanInt(sc)

	graph := make([][]int, nNodes)
	for i := 0; i < nConns; i++ {
		a, b := scanInt(sc), scanInt(sc)
		graph[a] = append(graph[a], b)
		graph[b] = append(graph[b], a)
	}

	groups := make([]int, nNodes)

	var setGroups func(int, int)
	setGroups = func(u int, groupId int) {
		if groups[u] > 0 {
			return
		}
		groups[u] = groupId

		for _, v := range graph[u] {
			setGroups(v, groupId)
		}
	}
	for i := 0; i < nNodes; i++ {
		setGroups(i, i+1)
	}

	nQuestions := scanInt(sc)

	w := bufio.NewWriter(os.Stdout)
	var ans string
	for i := 0; i < nQuestions; i++ {
		a, b := scanInt(sc), scanInt(sc)
		if groups[a] == groups[b] {
			ans = "yes"
		} else {
			ans = "no"
		}
		fmt.Fprintln(w, ans)
	}
	w.Flush()
}

func scanInt(sc *bufio.Scanner) int {
	sc.Scan()
	v, _ := strconv.Atoi(sc.Text())
	return v
}

C++: /**
 */

/*
 * test case 1
 2 1 1 2 1 1 2  
 test case 2
 4 4 1 2 1 3 2 4 3 4 1 1 2   
 */


#include <iostream>
#include <vector>
#include <queue>
using namespace std;
vector< vector<int> > rel;
vector<bool> visited;
int n, m, q;
int dest = 0;


bool fre1(int j) 
{
	for (int i=0;i<rel[j].size();i++)
	{
		int kk = rel[j][i];
		if (kk==dest) return true;
		if (visited[kk])continue;
		visited[kk]=true;
		if(fre1(kk))return true;
	}
	return false;
}

/**
 * preserve a priority que of nodes with the most connections. 
 * if there is a node with only 2 connections go look for the other one.
 */

priority_queue< pair<int, int> > pq;


bool fre3(int start) 
{
	for (int i=0;i<rel[start].size();i++)
	{
		int cand = rel[start][i];
		if (cand==dest) return true;
		if (visited[cand])continue;
		visited[cand]=true;
		int point = rel[cand].size();
		if (point == 1) continue;
		if (point == 2) {
			if (fre3(cand)) return true;
		} else {
			pq.push(pair<int, int>(point, cand));
		}
	}
	return false;
}


bool fre2(int start) 
{
	pq.push(pair<int,int>(0, start));
	while (pq.size())
	{
		pair<int, int> p = pq.top();
		pq.pop();
		start = p.second;
		if (fre3(start)) return true;
	}
	return false;
}


int main()
{
	cin >> n;
	rel.resize(n+1);
	cin >> m;
	for (int i=1;i<=m;i++){
		int j, k;
		cin >> j >> k;
		rel[j].push_back(k);
		rel[k].push_back(j);
	}

	cin >> q;
	for (int i=1;i<=q;i++){
		int start;
		cin >> start >> dest;
		visited.clear();
		visited.resize(n+1);
		cout << (fre2(start) ? "yes" : "no") << endl;
	}

	return 0;
}

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

vector<int> par(100005,-1);

void initialize(int n){
	for (int i=0;i<n;i++){
		par[i]=i;
	}
	return;
}

int root(int x){
	if (x==par[x]){
		return x;
	}else{
		return par[x]=root(par[x]);
	}
}

bool find(int x,int y){
	return root(x)==root(y);
}

void uni(int x,int y){
	x=root(x);
	y=root(y);
	if(x==y){
		return;
	}else{
		par[x]=y;
	}
}

int main(){
	int n,m,q,i,j;
	int s,t;
	
	cin >> n >> m;
	
	initialize(n);
	
	for(i=0;i<m;i++){
		cin >> s >> t;
		uni(s,t);
	}
	
	cin >> q;
	
	for (i=0;i<q;i++){
		cin >> s >> t;
		if (find(s,t)){
			cout << "yes" <<endl;
		}else{
			cout << "no" <<endl;
		}
	}
	return 0;
}

C++: #include<cstdio>
#include<cstring>
#include<vector>
#include<queue>
#include<algorithm>
#include<cmath>
#include<climits>
#include<string>
#include<set>
#include<numeric>
#include<map>
#include<iostream>
using namespace std;
#define rep(i,n) for(int i = 0;i<((int)(n));i++)
#define reg(i,a,b) for(int i = ((int)(a));i<=((int)(b));i++)
#define irep(i,n) for(int i = ((int)(n)-1);i>=0;i--)
#define ireg(i,a,b) for(int i = ((int)(b));i>=((int)(a));i--)
typedef long long ll;
typedef pair<ll, ll> mp;

//Union-Find??¨

int par[100000];//?±????????????£???
vector<vector<int> >v(100000);

int find(int x){
	if(par[x]==x)return x;
	return par[x]=find(par[x]);//????????§????????§???
}

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

void unify(int x,int y){
	x=find(x);
	y=find(y);
	if(x==y)return;
	par[x]=y;
}

int main(void){
	int n,m,f1,f2,q,s[10000],t[10000];
	cin>>n>>m;
	rep(i,n)par[i]=i;//union-find??¨????????????
	rep(i,m){
		cin>>f1>>f2;
		unify(f1,f2);
	}
	cin>>q;
	rep(i,q)cin>>s[i]>>t[i];//query
	rep(i,q)if(same(s[i],t[i])){
		cout<<"yes"<<endl;
	}else{
		cout<<"no"<<endl;
	}
	return 0;
}

C++: #include <cstdio>
#include <set>
#include <queue>
#include <vector>

void assignGroup(const std::vector<std::set<int>>& firend_relationships, std::vector<int>& group)
{
  int current_group = 1;
  std::queue<int> next_queue;
  std::set<int> searched_set;

  for (int i = 0; i < (int)firend_relationships.size(); ++i)
  {
    // Any group is the id assigned, then skip it
    if (searched_set.count(i) != 0)
      continue;

    group[i] = current_group;
    next_queue.push(i);

    while (!next_queue.empty())
    {
      // Remove from waiting list
      int current_id = next_queue.front();
      next_queue.pop();
      // Add to searched list
      searched_set.insert(current_id);

      // Add to waiting list which is not serached yet
      std::set<int>::const_iterator itr;
      for (itr = firend_relationships[current_id].begin();
           itr != firend_relationships[current_id].end();
           ++itr)
      {
        // Ignore searched ones
        if (searched_set.count(*itr) != 0)
          continue;

        group[*itr] = current_group;
        next_queue.push(*itr);
      }
    }

    // Assign the different group number
    ++current_group;
  }
}

bool isConnected(const int& id_from, const int& id_to, const std::vector<int>& group)
{
  return group[id_from] == group[id_to];
}

int main()
{
  int n, m;
  scanf("%d%d", &n, &m);

  std::vector<std::set<int>> firend_relationships;
  std::vector<int> group;
  firend_relationships.resize(n);
  group.resize(n);
  for (int i = 0; i < m; ++i)
  {
    int id1, id2;
    scanf("%d%d", &id1, &id2);
    firend_relationships[id1].insert(id2);
    firend_relationships[id2].insert(id1);
  }

  assignGroup(firend_relationships, group);

  int q;
  scanf("%d", &q);
  for (int i = 0; i < q; ++i)
  {
    int id1, id2;
    scanf("%d%d", &id1, &id2);
    if (isConnected(id1, id2, group))
      printf("yes\n");
    else
      printf("no\n");
  }

  return 0;
}

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