Go: package main

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

var (
	n     int
	G     [100000][]int
	color [100000]*int
)

func dfs(r int, c int) {
	S := Stack{}
	S.Push(r)
	color[r] = &c
	for !S.IsEmpty() {
		u := S.Pop()
		for i := 0; i < len(G[u]); i++ {
			v := G[u][i]
			if color[v] == nil {
				color[v] = &c
				S.Push(v)
			}
		}
	}
}

func assignColor() {
	id := 1
	for i := 0; i < n; i++ {
		color[i] = nil
	}
	for u := 0; u < n; u++ {
		if color[u] == nil {
			id++
			dfs(u, id)
		}
	}
}

func main() {
	sc := bufio.NewScanner(os.Stdin)
	sc.Split(bufio.ScanWords)
	sc.Scan()
	n, _ = strconv.Atoi(sc.Text())
	sc.Scan()
	r, _ := strconv.Atoi(sc.Text())

	for i := 0; i < r; i++ {
		sc.Scan()
		s, _ := strconv.Atoi(sc.Text())
		sc.Scan()
		t, _ := strconv.Atoi(sc.Text())
		G[s] = append(G[s], t)
		G[t] = append(G[t], s)
	}
	assignColor()
	sc.Scan()
	qNum, _ := strconv.Atoi(sc.Text())
	for i := 0; i < qNum; i++ {
		sc.Scan()
		s, _ := strconv.Atoi(sc.Text())
		sc.Scan()
		t, _ := strconv.Atoi(sc.Text())
		if color[s] == color[t] {
			fmt.Println("yes")
		} else {
			fmt.Println("no")
		}
	}
}

// Stack is Stack
type Stack struct {
	stack []int
}

// Push new value
func (stack *Stack) Push(val int) {
	stack.stack = append(stack.stack, val)
}

// Pop new value
func (stack *Stack) Pop() int {
	val := stack.stack[len(stack.stack)-1]
	stack.stack = stack.stack[0 : len(stack.stack)-1]
	return val
}

// IsEmpty return true when stack is empty
func (stack *Stack) IsEmpty() bool {
	return len(stack.stack) == 0
}

C++: #include<iostream>
#include<vector>
#include<stack>
#include<queue>
#include<algorithm>

struct node {
	int parent;
	std::vector<int> relation;
};

void dfs(std::vector<node> &n) {
	std::stack<int> s;
	std::vector<int> d(n.size()), dd(n.size());
	for (size_t i = 0; i < n.size(); i++) {
		n[i].parent = -1;
		if (dd[i] == 1)continue;
		std::fill(d.begin(), d.end(), 0);
		s.push(i);
		while (s.size() != 0) {
			int num = s.top(); s.pop();
			d[num] = 1;
			dd[num] = 1;
			for (std::vector<int>::iterator it = n[num].relation.begin(); it != n[num].relation.end(); it++) {
				if (d[*it] == 1) {
					n[num].relation.erase(it);
					it--;
				} else {
					s.push(*it);
					d[*it] = 1;
					n[*it].parent = num;
					std::vector<int>::iterator itt= std::find(n[*it].relation.begin(), n[*it].relation.end(), num);
					if (itt != n[*it].relation.end()) {
						n[*it].relation.erase(itt);
					}
				}
			}
		}
	}
}

void makeparent(std::vector<node> &n) {
	std::queue<int> q;
	for (size_t i = 0; i < n.size(); i++) {
		n[i].parent = -1;
	}
	for (size_t i = 0; i < n.size(); i++) {
		q.push(i);
		int parent = i;
		while (q.size() != 0) {
			parent = q.front(); q.pop();
			for (size_t j = 0; j < n[parent].relation.size(); j++) {
				q.push(n[parent].relation[j]);
				n[n[parent].relation[j]].parent = parent;
			}
		}
	}
}

bool isconnect(std::vector<node> n, int from, int to) {
	std::stack<int> s;
	while (n[from].parent != -1) {
		from = n[from].parent;
		if (from == to) return true;
	}
	s.push(from);
	while(s.size() != 0) {
		from = s.top(); s.pop();
		for (std::vector<int>::iterator it = n[from].relation.begin(); it != n[from].relation.end(); it++) {
			if (to == *it) return true;
			s.push(*it);
		}
	}
	return false;
}

int main() {
	int people, relation;

	std::cin >> people >> relation;

	std::vector<node> n(people);

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

	dfs(n);
	//makeparent(n);

	/*
	for (size_t i = 0; i < n.size(); i++) {
	std::cout << i << " " << n[i].parent << std::endl;
	}
	*/
	/*
	for (size_t i = 0; i < n.size(); i++) {
		for (size_t j = 0; j < n[i].relation.size(); j++) {
			std::cout << i << n[i].relation[j] << std::endl;
		}
	}
	//*/

	int question;
	std::cin >> question;

	for (int i = 0; i < question; i++) {
		int from, to;
		std::cin >> from >> to;
		if (isconnect(n, from, to)) {
			std::cout << "yes" << std::endl;
		} else {
			std::cout << "no" << std::endl;
		}
	}

	return 0;
}

C++: #include <cstdio>
#include <iostream>
#include <algorithm>
#include <vector>
using namespace std;
int N,M,Q;
int rank[100001],par[100001];
int find(int x){
  if(par[x]==x)return x;
  else return par[x]=find(par[x]);
}
void unite(int x,int y){
  x=find(x);
  y=find(y);
  if(x==y)return ;

  if(rank[x]<rank[y]){
    par[x]=y;
  }
  else{
    par[y]=x;
    if(rank[x]==rank[y])rank[x]++;
  }
}

bool same(int x,int y){
  return find(x)==find(y);
}
int main(){
  cin >> N >> M;
  for(int i=0;i<N;i++){
    par[i]=i;
    rank[i]=0;
  }
  for(int i=0;i<M;i++){
    int u,v;
    cin >> u >> v;
    unite(u,v);
  }
  cin >> Q;
  for(int i=0;i<Q;i++){
    int s,d;
    cin >> s >> d;
    if(same(s,d))printf("yes\n");
    else printf("no\n");
  }
  return 0;
}

C++: #include <stdio.h>
#include <stack>
using namespace std;
int G[1000][1000];
int vis[100000];
int n;

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

int main()
{
    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)) printf("yes\n");
        else printf("no\n");
    } 
    return 0;
}

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

using namespace std;

void calc(int n,int s,vector<int> adj[],vector<int> &u){
	u[s] = s;
	vector<bool> visited(n,false);
	priority_queue<int> np;
	np.push(s);
	while(!np.empty()){
		int now = np.top(); np.pop();
		visited[now] = true;
		for(int i = 0; i < adj[now].size(); ++i){
			int next = adj[now][i];
			if(visited[next])continue;
			np.push(next);
			u[next] = s;
		}
	}
	return;
}


int main(){
	int n,m; cin >> n >> m;
	vector<int> adj[n];
	for(int i = 0; i < m; ++i){
		int s,t; cin >> s >>t;
		adj[s].push_back(t);
		adj[t].push_back(s);
	}
	vector<int> u(n,-1);
	for(int i = 0; i < n; i++){
		if(u[i] != -1)continue;
		calc(n,i,adj,u);
	}
	int q; cin >> q;
	for(int i = 0; i < q; i++){
		int s,t; cin >> s >> t;
		if(u[s] == u[t])cout << "yes" << endl;
		else cout << "no" << endl;
	}
	return 0;
}

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

vector<int> list[100000];
int n,m;

bool bfs(int s, int t){

  bool used[m];
  for(int i=0;i<m;i++) used[i]=false; //初期化

  queue<int> Q;
  Q.push(s); used[s]=true;

  while(!Q.empty()){
    int k=Q.front(); Q.pop();
    if(k==t){return true;}
    for(int i=0;i<list[k].size();i++){
      int temp=list[k][i];
      if(!used[temp]){ //未訪問なら
        Q.push(temp); used[temp]=true;
      }
    }
  }
  return false;
}
int main(){

  cin>>n>>m;

  for(int i=0;i<m;i++){
    int u,v; cin>>u>>v;
    list[u].push_back(v);
    list[v].push_back(u);
  }

  int q; cin>>q;

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

}