Go: package main

import (
	"fmt"
)

var n, m int
var g [][]int
var color []int

func main() {
	fmt.Scan(&n, &m)
	g = make([][]int, n) // SNSの関係を表すグラフ
	for i := 0; i < m; i++ {
		var a, b int
		fmt.Scan(&a, &b)
		g[a] = append(g[a], b) // 無向重みなしグラフ
		g[b] = append(g[b], a)
	}
	color = make([]int, n) // 各ノードにつける色
	for i := 0; i < len(color); i++ {
		color[i] = -1 // 初期化しておく
	}
	type query struct {
		s, t int
	}
	var Q int
	fmt.Scan(&Q)
	qs := make([]query, Q)
	for i := 0; i < Q; i++ {
		fmt.Scan(&qs[i].s, &qs[i].t)
	}
	// fmt.Println("n", n, "m", m, "g", g, "Q", Q, "qs", qs)
	// 全ての頂点からdfsする
	id := 1
	for u := 0; u < n; u++ {
		if color[u] == -1 {
			dfs(u, id)
			id++
		}
	}
	// fmt.Println("color", color)
	for i := 0; i < Q; i++ {
		if color[qs[i].s] == color[qs[i].t] {
			fmt.Println("yes")
		} else {
			fmt.Println("no")
		}
	}
}

func dfs(v, c int) {
	// fmt.Printf("dfs(v %d, c %d) en:\n", v, c)
	color[v] = c
	for _, vv := range g[v] {
		// fmt.Printf("  v %d, g[v] %v, vv %d\n", v, g[v], vv)
		if color[vv] == -1 {
			dfs(vv, c)
		}
	}
}

C++: #include <iostream>
#include <fstream>

#include <cassert>
#include <climits>

#include <string.h>

#include <vector>
#include <map>
#include <stack>
#include <deque>

int n, m;
int q;

std::vector< std::vector<int> > connection;
std::vector<int> color;

void breadthFirstSearch(int first, int id)
{
    std::deque<int> dq;
    assert(color[first] == -1);

    dq.push_back(first);
    color[first] = id;

    while (! dq.empty())
    {
        int current = dq.front();
        dq.pop_front();

        for (std::vector<int>::iterator it = connection[current].begin(); it != connection[current].end(); ++it)
        {
            if (color[(*it)] > -1)
            {
                continue;
            }

            dq.push_back(*it);
            color[(*it)] = id;
        }
    }
}

int main()
{
    std::cin >> n >> m;
    for (int i = 0; i < n; ++i)
    {
        std::vector<int> line;
        connection.push_back(line);

        color.push_back(-1);
    }

    for (int i = 0; i < m; ++i)
    {
        int a, b;
        std::cin >> a >> b;

        connection[a].push_back(b);
        connection[b].push_back(a);
    }

    int id = 0;
    for (int i = 0; i < n; ++i)
    {
        if (color[i] == -1)
        {
            breadthFirstSearch(i, id++);
        }
    }

    std::cin >> q;
    for (int i = 0; i < q; ++i)
    {
        int a, b;
        std::cin >> a >> b;
        std::string ans = (color[a] == color[b]) ? "yes" : "no";
        std::cout << ans << std::endl;
    }

    return 0;
}

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

#define REP(i, n) for(int i=0;i<(int)(n);i++)
#define ALL(x) (x).begin(),(x).end()
const int INF = 1e9;

using namespace std;
int n, m;
struct node {
    int id;
    int parent;
};

node person[100000];

int find(node x, vector<int> path){
    if(x.parent == -1){
        REP(i, path.size())
            person[path[i]].parent = x.id;
        return x.id;
    }
    else{
        path.push_back(x.id);
        return find(person[x.parent], path);
    }
}

void marge(node x, node y){
    vector<int> xpath, ypath;
    int x_id = find(x, xpath);
    int y_id = find(y, ypath);
    if(x_id == y_id)
        return;
    else
        person[y_id].parent = x_id;
    return;
}

bool judge(node x, node y){
    vector<int> xpath, ypath;
    return find(x, xpath) == find(y, ypath);
}

int main() {
    cin >> n >> m;
    REP(i, n){
        person[i].id = i;
        person[i].parent = -1;
    }
    REP(i, m){
        int s, t;
        cin >> s >> t;
        if(person[t].parent == -1)
            person[t].parent = person[s].id;
        else if(person[s].parent == -1)
            person[s].parent = person[t].id;
        else marge(person[s], person[t]);
    }
    int q;
    cin >> q;
    REP(i, q){
        int s, t;
        cin >> s >> t;
        if(judge(person[s], person[t]))
            cout << "yes" << endl;
        else
            cout << "no" << endl;
    }
    return 0;
}

C++: #include <iostream>

using namespace std;

// int A[N][N];
vector<vector<int>> A;
int n;

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

int main() {
    A.resize(N);
    for (int i = 0; i < N; ++i)
        A[i].resize(N);

    int m;
    cin >> n >> m;
    for (int i = 0; i < m; ++i) {
        int s, t;
        cin >> s >> t;
        A[s][t] = 1;
    }

    int q;
    cin >> q;
    for (int j = 0; j < q; ++j) {
        int x, y;
        cin >> x >> y;

        if (dfs(x, y)) {
            cout << "yes";
        } else {
            cout << "no";
        }
        cout << endl;
    }

    return 0;
}

C++: #include<iostream>
#include<vector>
#include<stack>
using namespace std;
const int MAX=100000;
const int NIL=-1;
int n;
vector<int>G[MAX]; //頂点を100000とする
                   //隣接リスト
int color[MAX];
void dfs(int r,int c){
  stack<int>S;
  S.push(r); //始点rをスタックに追加
  color[r]=c; //色を入れる
  while(!S.empty()){ //スタックが空でない間
    int u=S.top();
    S.pop();
    for(int i=0;i<G[u].size();i++){
      //頂点uに隣接する頂点vを探索
      int v=G[u][i];
      if(color[v]==NIL){
	color[v]=c;
	S.push(v); //id(色)は変わらない
      }
    }
  }
}
int main(){
  int s,t,m,q;
  scanf("%d%d",&n,&m);
  for(int i=0;i<m;i++){
    scanf("%d%d",&s,&t);
    G[s].push_back(t); //sからtへ辺
    G[t].push_back(s); //tからsへ辺
  }
  int id=1; //colorに入れる色(情報)
  for(int i=0;i<n;i++){
    color[i]=NIL; //すべてにNIL
  }
  for(int u=0;u<n;u++){
    if(color[u]==NIL) dfs(u,id++); //id(色)にかぶりがないように
  }
  scanf("%d",&q);
  for(int i=0;i<q;i++){
    scanf("%d%d",&s,&t);
    if(color[s]==color[t]) printf("yes\n");
    else printf("no\n");
  }
  return 0;
}

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