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<algorithm>
#include<vector>
#include<queue>
#define MAX 100001
using namespace std;
int n;
int color[MAX] = {0};
vector<int> number[MAX];
void Connected_Components(void){
    int col = 0;
    for(int i=0;i<n;i++){
        if(color[i]==0){
            queue<int> Number_of_vertices;
            Number_of_vertices.push(i);
            color[i] = ++col;
            while(!Number_of_vertices.empty()){
                int v = Number_of_vertices.front();
                Number_of_vertices.pop();
                //cout << v << endl;
                for(int j=0;j<number[v].size();j++){
                    if(color[number[v][j]]==0){
                        color[number[v][j]] = col;
                        //cout << color[j] << endl;
                        Number_of_vertices.push(number[v][j]);
                    }
                }
            }
        }
    }
}
void input(void){
    int m;
    cin >> n >> m;
    for(int i=0;i<n;i++){
        number[i].push_back(i);
    }
    for(int i=0;i<m;i++){
        int id,fre;
        cin >> id >> fre;
        number[id].push_back(fre); 
        number[fre].push_back(id);
    }
    // for(int i=0;i<n;i++){
    //     for(int j=0;j<number[i].size();j++){
    //         cout << number[i][j] << ' ';
    //     }
    //     cout << endl;
    // }
}
void question(void){
    int q;
    cin >> q;
    for(int i=0;i<q;i++){
        int id_1,id_2;
        cin >> id_1 >> id_2;
        if(color[id_1]==color[id_2]){
            cout << "yes" << endl;
        }else{
            cout << "no" << endl;
        }
    }
}
int main(void){
    input();
    Connected_Components();
    question();
    return 0;
}

C++: #include <iostream>
#include <vector>
#include <set>

using namespace std;

const int N = 100000;
// int A[N][N];
vector<set<int>> A;


bool dfs(int s, int t) {
    auto& S = A[s];
    if (S.find(t) != S.end()) {
        return true;
    }
    for (auto i : S) {
        if (i != t) {
            if (dfs(i, t)) {
                return true;
            }
        }
    }
    return false;
}

int main() {
    A.resize(N);

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

    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<stack>
#include<queue>
#include<vector>
#include<iostream>
#include<algorithm>
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;
}

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

using namespace std;

#define MAX 100000
#define NIL -1

int n;
int color[MAX];
vector<int> G[MAX];


void dfs(int u, int id){
  
  stack<int> S;
  S.push(u);
  color[u] = id;

  int present;
  while( !S.empty() ){
    present = S.top();
    S.pop();

    for(int i=0;i<G[present].size();i++){
      int v = G[present][i];
      if( color[v] == NIL ){
        color[v] = id;
        S.push(v);
      }    
    }  
  }
}

void assignColor(){
 
  for(int i=0;i<n;i++){
    color[i] = NIL;
  } 

  int id = 0;
  for(int u=0;u<n;u++){
    if(color[u] == NIL){
      dfs(u,id);
      id = id + 1;
    }
  }
}

int main(void){

  int m;
  cin >> n >>  m;

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

  assignColor();

  int q;
  cin >> q;

  int s,t;
  for(int i=0;i<q;i++){
    cin >> s >> t;
    if( color[s] == color[t] ){
      cout << "yes" << endl;
    }else{
      cout << "no"<< endl;;
    } 
  }

  return 0;
}

C++: #include<stdio.h>
#include<queue>

#define MAX 100000

int G[MAX+1][MAX+1];
int n, m;
std::queue<int> Q;

bool bfs(int src, int dest) {
    bool C[MAX];
    for (int i = 0; i < n; ++i) C[i] = false;

    Q.push(src);
    while(!Q.empty()) {
        int cur = Q.front();Q.pop();
        for (int i = 0; i < n; ++i) {
            if (G[cur][i] == 0) continue;
            if (C[i]) continue;
            if (i == dest) return true;
            Q.push(i);
            C[i] = true;
        }
    }

    return false;
}

int main() {
    scanf("%d %d", &n, &m);
    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 u,k;
    //    scanf("%d %d", &u, &k);
    //    G[u][k] = 1;
    //    G[k][u] = 1;
    //}

    //int q;
    //scanf("%d", &q);
    //for (int i = 1; i <= q; ++i) {
    //    int s,d;
    //    scanf("%d %d", &s, &d);
    //    bfs(s, d) ? printf("yes\n") : printf("no\n");
    //}

    return 0;
}