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 <stdio.h>
#include <stdlib.h>
#include <iostream>
#include <vector>
#include <stack>
#include <string.h>
#define rep(i, n) for(int i=0;i<n;i++)
#define FOR(i, j, n) for(int i=j;i<n;i++)
#define NOT_FOUND 0
using namespace std;

vector<int> graph[100001];
int memo[100001];

int dfs(int start, int label) {
    stack<int> stack;
    stack.push(start);
    memo[start] = label;

    while(!stack.empty()) {
        int v = stack.top();
        stack.pop();
        vector<int> edges = graph[v];

        rep(i, edges.size()) {
            int next = edges[i];
            if (memo[next] == 0) {
                memo[next] = label;
                stack.push(next);
            }
        }
    }
    return 1;
}

int main() {
    int n, m;
    cin >> n >> m;

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

    memset(memo, 0, sizeof(memo));
    int id = 1;
    rep(i, n) {
        if (memo[i] == 0) {
            dfs(i, id++);
        }
    }

    int q;
    cin >> q;
    rep(i, q) {
        int s, d;
        cin >> s >> d;
        if (memo[s] == memo[d]) {
            cout << "yes" << endl;
        } else {
            cout << "no" << endl;
        }
    }
    return 0;
}

C++: #include <iostream>
#include <cstdio>
#define MAX 100000

using namespace std;

int main(){
  int a[MAX]={};
  int n,m; cin>>n>>m;
  int s,t;
  int group=1;
  for(int i=0;i<m;i++){
    scanf("%d %d",&s,&t);
    if(a[s]==0 && a[t]==0){
      a[s]=a[t]=group;
      group++;
    }else if(a[s]==0){
      a[s]=a[t];
    }else if(a[t]==0){
      a[t]=a[s];
    }else{
      int tmp=a[t];
      a[t]=a[s];
      for(int j=0;j<n;j++){
        if(a[j]==tmp) a[j]=a[s];
      }
    }
  }

  int q; cin>>q;
  for(int i=0;i<q;i++){
    cin>>s>>t;
    if(a[s]==a[t]&&a[s]*a[t]!=0){
      printf("yes\n");
    }else{
      printf("no\n");
    }
  }

}

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;

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);
        queue<int> q;
        q.push(id);
        bool found = false;
        while (!q.empty()) {
            int per = q.front();
            q.pop();
            if (visited[per])
                continue;
            if (per == f) {
                found = true;
                break;
            }
            visited[per] = true;
            for (int j = 0; j < sns[per].size(); ++j) {
                q.push(sns[per][j]);
            }
        }
        if (found)
            printf("yes\n");
        else
            printf("no\n");
    }

    return 0;
}

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

bool search(vector<int> member,int x){
  for(int i=0; i<member.size(); i++){
    if(member[i] == x)
      return true;
  }
    return false;
}

int main(){
  int n,m,join[10000],s,t;
  vector<int> group[10000];
  cin >> n >> m;

  for(int i=0; i<n; i++)
    join[i] = i;
    
  for(int i=0; i<m; i++){
    bool flag = search(group[join[t]],s);

    if(!flag){
      group[join[s]].push_back(t);
      
      for(int j=0; j<group[t].size(); j++)
	join[group[t][j]]=join[s];
	  
      join[t] = join[s];
    }
  }

  int q;
  cin >> q;
  
  bool answer[10000];
  for(int i=0; i<q; i++){
    cin >> s >> t;
    
    if(join[s] == join[t])
      answer[i]=true;
    else
      answer[i]=false;
  }

  for(int i=0; i<q; i++){
    if(answer[i])
      cout << "yes\n";
    else
      cout << "no\n";
  }
}

C++: #include <cstdio>
#include <vector>
#include <algorithm>
#include <queue>
#include <utility>

using namespace std;

template <class T>
using lp_queue=priority_queue<T, vector<T>, greater<T>>;

using Weight=int;
using DArray=vector<Weight>;
using DMatrix=vector<DArray>;

static const Weight INF=1<<29;

struct Edge {
    size_t src, dst;
    Weight weight;
    Edge() {}
    Edge(size_t src, size_t dst, Weight weight=1):
        src(src), dst(dst), weight(weight)
    {}
};

bool operator<(const Edge &e, const Edge &f) {
    if (e.weight != f.weight) {
        return e.weight > f.weight;
    } else {
        return e.src!=f.src? e.src<f.src : e.dst<f.dst;
    }
}

using Edges=vector<Edge>;
using Vertex=vector<Edge>;
using Graph=vector<Vertex>;

void join(Graph &g, size_t s, size_t d, Weight w=1) {
    // non-directed
    g[s].push_back(Edge(s, d, w));
    g[d].push_back(Edge(d, s, w));
}

void connect(Graph &g, size_t s, size_t d, Weight w=1) {
    // directed
    g[s].push_back(Edge(s, d, w));
}

vector<Weight> shortest_distance(const Graph &g, size_t s) {
    /* Dijkstra */
    size_t V=g.size();
    vector<Weight> d(V, INF); d[s]=0;

    lp_queue<pair<Weight, size_t>> q; q.push(make_pair(0, s));
    while (!q.empty()) {
        pair<Weight, size_t> p=q.top(); q.pop();
        size_t v=p.second;
        if (d[v] < p.first) continue;

        for (const Edge &e: g[v])
            if (d[e.dst] > d[v] + e.weight) {
                d[e.dst] = d[v] + e.weight;
                q.push(make_pair(d[e.dst], e.dst));
            }
    }
    return d;
}

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

    Graph g(n);
    for (size_t i=0; i<m; ++i) {
        size_t s, t;
        scanf("%zu %zu", &s, &t);

        join(g, s, t);
    }

    size_t q;
    scanf("%zu", &q);

    for (size_t i=0; i<q; ++i) {
        size_t s, t;
        scanf("%zu %zu", &s, &t);

        printf("%s\n", shortest_distance(g, s)[t]<INF? "yes":"no");
    }

    return 0;
}