Go: package main

import (
	"bufio"
	"container/list"
	"fmt"
	"os"
	"strconv"
)

//util
var sc = bufio.NewScanner(os.Stdin)

func nextStr() string {
	sc.Scan()
	return sc.Text()
}

func nextInt() int {
	sc.Scan()
	i, e := strconv.Atoi(sc.Text())
	if e != nil {
		panic(e)
	}
	return i
}

func printList(list []int) {
	n := len(list)
	buf := bufio.NewWriter(os.Stdout)
	for _, v := range list[0 : n-1] {
		buf.Write([]byte(fmt.Sprintf("%d ", v)))
	}
	buf.Write([]byte(fmt.Sprintf("%d\n", list[n-1])))
	buf.Flush()
}

func max(a, b int) int {
	if a > b {
		return a
	} else {
		return b
	}
}

func min(a, b int) int {
	if a > b {
		return b
	} else {
		return a
	}
}

//solve
const (
	MAX = 100000
	NIL = -1
)

var (
	n, m, q, s, t int
	G             [MAX][]int //連結リスト
	color         [MAX]int
)

func dfs(r int, c int) {
	S := list.New()
	S.PushFront(r)
	color[r] = c
	for S.Len() != 0 {
		u := S.Remove(S.Front()).(int)
		for i := 0; i < len(G[u]); i++ {
			v := G[u][i]
			if color[v] == NIL {
				color[v] = c
				S.PushFront(v)
			}
		}
	}
}

//幅優先探索で、頂点を色付け
func assignColor() {
	id := 1
	for i := 0; i < n; i++ {
		color[i] = NIL
	}
	for i := 0; i < n; i++ {
		if color[i] == NIL {
			id++
			dfs(i, id)
		}
	}
}

func main() {
	sc.Split(bufio.ScanWords)
	n, m = nextInt(), nextInt()
	for i := 0; i < m; i++ {
		s, t = nextInt(), nextInt()
		if i == 0 {
			G[s] = make([]int, 0)
			G[t] = make([]int, 0)
		}
		G[s] = append(G[s], t)
		G[t] = append(G[t], s)

	}
	assignColor()
	q = nextInt()
	for i := 0; i < q; i++ {
		s, t = nextInt(), nextInt()
		if color[s] == color[t] {
			fmt.Println("yes")
		} else {
			fmt.Println("no")
		}
	}

}

C++: #include<iostream>
using namespace std;
#include<stdio.h>

typedef struct box { int val; box *prev, *next; } box_t;

box_t* init()
{
    box_t* head = new box_t;
    head->val = -1;
    head->next = NULL;
    head->prev = NULL;
    return head;
}

box_t* make_tail(box_t* head)
{
    box_t* tail = new box_t;
    tail->val = -1;
    head->next = tail;
    tail->next = NULL;
    tail->prev = head;
    return tail;
}

bool isEmpty(box_t* head, box_t* tail)
{
    return (head->next == tail ? true : false);
}

box_t* f_insert(box_t* head, int data)
{
    box_t* box = new box_t;
    box->val = data;
    box->next = head->next;
    box->prev = head;
    head->next->prev = box;
    head->next = box;
    return box;
}

int b_pop(box_t* tail)
{
    if(!(tail->prev->prev)) return -1;
    box_t* box = tail->prev;
    int val;
    val = tail->prev->val;
    tail->prev = box->prev;
    box->prev->next = tail;
    delete box;
    return val;
}

void clear(box_t* head, box_t* tail)
{
    box_t* box1 = head->next;
    box_t* box2;
    if(box1 == tail) return;
    while(box1 != tail){
        box2 = box1->next;
        delete box1;
        box1 = box2;
    };
    head->next = tail;
    tail->prev = head;
    return;
}

int main()
{
    int G[2800][100];
    int *dist;

    box_t* head = init();
    box_t* tail = make_tail(head);

    int n, i, j, e, q, v1, v2;
    scanf("%d", &n);

	dist = new int [n];

    for(i = 0; i < n; i++){
        for(j = 0; j < n; j++){ G[i][j] = 0; } }
    int m;
    scanf("%d", &m);
    for(int k = 0; k < m; k++){
        scanf("%d %d", &i, &j);
        G[i][0]++; G[j][0]++;
        G[i][G[i][0]] = j;
        G[j][G[j][0]] = i;
    }
    scanf("%d", &q);
    int self, friends;
    bool is_connected;

    for(int k = 0; k < q; k++){
        for(j = 0; j < n; j++) dist[j] = -1;

        scanf("%d %d", &self, &friends);
        f_insert(head, self);
        dist[self] = 0;
        is_connected = false;

        while(1){
            v1 = b_pop(tail);
            e = G[v1][0];
            for(i = 1; i <= e; i++){
                v2 = G[v1][i];
                if(dist[v2] < 0){
                    dist[v2] = dist[v1] + 1;
                    f_insert(head, v2);
                }
            }
            if(dist[friends] > 0){
                is_connected = true;
                break;
            }
            if(isEmpty(head, tail)) break;
        };
        if(is_connected){ printf("yes\n"); }else{ printf("no\n"); }
        if(!isEmpty(head, tail)) clear(head, tail);
    }

	delete [] dist;

    return 0;
}

C++: #include<iostream>
#include<vector>
#include<stack>
using namespace std;
vector<int>v[100000];
int color[100000];
void dpf(int a,int c) {
    color[a] = c;
	stack<int>s;
	for (int i = 0; i < v[a].size(); i++) {
		int t = v[a][i];
		s.push(t);
		color[t] = c;
	}
	while (!s.empty())
	{
		int k = s.top();
		s.pop();
		for (int i = 0; i < v[k].size(); i++) {
			
			int t = v[k][i];
			if (color[t] == 0) {
				s.push(t);
				color[t] = c;
			}
		}
	}
}
void setcolor(int n) {
	int t=1;
	for (int i = 0; i < n; i++) {
		if (color[i] == 0) {
			dpf(i, t++);
		}
	}
}
int main(void) {
	int n,k;
	cin >> n;
	cin >> k;
	for (int i = 0; i < k; i++) {
		int a, b;
		cin >> a >> b;
		v[a].push_back(b);
		v[b].push_back(a);
	}
	setcolor(n);
	int q;
	cin >> q;
	for (int i = 0; i < q; i++) {
		int a, b;
		cin >> a >> b;
		if (color[a]==color[b])
		{
			cout << "yes";
		}
		else {
			cout << "no";
		}
		cout << endl;
	}
}

C++: #include<iostream>
#include<vector>
using namespace std;
vector<vector<int>> G(100);
vector<int> c(100);
void dfs(int s, int x){
    if(c[s]) return;
    c[s]=x;
    for(auto a:G[s]) dfs(a,x);
}
int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    int n,m;
    cin>>n>>m;
    for(int i=0;i<m;++i){
        int a,b;
        cin>>a>>b;
        G[a].push_back(b);
        G[b].push_back(a);
    }
    for(int i=0;i<n;++i) dfs(i,i+1);
    int q;
    cin>>q;
    for(int i=0;i<q;++i){
        int a,b;
        cin>>a>>b;
        cout<<(c[a]-c[b]?"no":"yes")<<endl;
    }
}

C++: #include <iostream>
#include <queue>
#include <cstdio>
#include <vector>
using namespace std;
#define MAX_N 100000
int n;

bool can_connect(int s,int t,const vector< vector<int> > &g) {
  bool visited[n];
  queue<int> que;
  for(int i=0;i<n;i++) visited[i] = false;
  while(!que.empty()) que.pop();

  visited[s] = true;
  que.push(s);
  while(!que.empty()) {
    int v = que.front(); que.pop();
    for(int i=0;i<g[v].size();i++) {
      if(!visited[g[v][i]]) {
        if(g[v][i] == t) return true;
        visited[g[v][i]] = true;
        que.push(g[v][i]);
      }
    }
  }
  return false;
}

int main() {
  int m,s,t,q;
  scanf("%d %d\n",&n,&m);
  vector< vector<int> > g(n);
  for(int i=0;i<m;i++) {
    scanf("%d %d",&s,&t);
    g[s].push_back(t);
    g[t].push_back(s);
  }
  /*
  for(int i=0;i<g.size();i++) {
    printf("%d : ",i);
    for(int j=0;j<g[i].size();j++) {
      printf("%d ",g[i][j]);
    }
    printf("\n");
  }
  */

  scanf("%d",&q);
  for(int i=0;i<q;i++) {
    scanf("%d %d",&s,&t);
    //printf("%d,%d: ",s,t);
    if(can_connect(s,t,g)){
      printf("yes\n");
    }
    else {
      printf("no\n");
    }
  }
}