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 <vector>
#include <stack>
#include <algorithm>
using namespace std;

#define MAX 100000

vector<int> G[MAX];
int cond[MAX], n;
stack<int> S;

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

void check(int x, int y)
{
	for (int i = 0; i < (int)G[x].size(); i++) {
		if (G[x][i] == y) {
			cout << "yes" << endl;
			return;
		}
	}
	for (int i = 0; i < (int)G[y].size(); i++) {
		if (G[x][i] == y) {
			cout << "yes" << endl;
			return;
		}
	}
	cout << "no" << endl;
}

void dfs(int x, int id)
{
	S.push(x);
	cond[x] = id;

	int i, v;
	while (!S.empty()) {
		int u = S.top();
		S.pop();
		for (i = 0; i < (int)G[u].size(); i++) {
			v = G[u][i];			
			if (cond[v] == 0) {				
				cond[v] = id;
				S.push(v);
			}
		}
	}
}

void searchFriends()
{
	int id = 1;
	for (int i = 0; i < n; i++)
		if (cond[i] == 0) dfs(i, id++);
}

int main()
{
	int m, q, u, v;
	cin >> n >> m;

	set(m);
	searchFriends();

	cin >> q;
	
	for (int i = 0; i < q; i++) {
		cin >> u >> v;
		check(u, v);
		/*if (cond[u] != 0 && cond[v] != 0 && cond[u] == cond[v])
			cout << "yes" << endl;
		else cout << "no" << endl;*/
	}
	return 0;
}

C++: #include<iostream>
#include<cstring>
#include<vector>
#include<stack>
#include<queue>
using namespace std;
#define maxn 100005
#define NIL -1

int n,m;
vector<int> G[maxn]; //邻接表
int color[maxn]; //编号（可以互相链接的两个节点编号相同）

void dfs(int r,int c) //给节点r分配编号c（深搜实现）（栈）
{
    stack<int> S;
    S.push(r);
    color[r]=c;
    while(!S.empty())
    {
        int u=S.top();S.pop(); //从栈顶取出
        for(int i=0;i<G[u].size();i++)
        {
            int v=G[u][i];
            if(color[v]==NIL) //如果该节点无编号
            {
                color[v]=c; //给其编号
                S.push(v); //压入栈
            }
        }
    }
}

void dfs_(int r,int c) //给节点r分配编号c（深搜实现）（递归）
{
    color[r]=c;
    for(int i=0;i<G[r].size();i++) //注意这里代码于上面的不同
    {
        int v=G[r][i];
        if(color[v]==NIL)
            {
                color[v]=c;
                dfs_(v,c);
            }
    }
}

void bfs(int r,int c) //给节点r分配编号c（广搜实现）
{
    queue<int> S;
    S.push(r);
    color[r]=c;
    while(!S.empty())
    {
        int u=S.front();S.pop(); //从队首取出
        for(int i=0;i<G[u].size();i++)
        {
            int v=G[u][i];
            if(color[v]==NIL)
            {
                color[v]=c;
                S.push(v); //加入队列中
            }
        }
    }
}

void assigncolor()
{
    int id=1;
    memset(color,NIL,sizeof(color)); //这里要记得初始化
    for(int u=0;u<n;u++)
        if(color[u]==NIL)
            dfs_(u,id++); //这里选取了广搜的方式给各个节点编号
}

int main()
{
    int s,t,q;
    cin>>n>>m;
    while(m--)
    {
        cin>>s>>t;
        G[s].push_back(t); //从顶点s向t画边
        G[t].push_back(s); //反过来连边
    }
    assigncolor();
    cin>>q;
    while(q--)
    {
        cin>>s>>t;
        if(color[s]==color[t]) cout<<"yes"<<endl;
        else cout<<"no"<<endl;
    }
    return 0;
}

C++: #include<iostream>
#include<iostream>
#include<vector>
#include<stack>
using namespace std;
static const int MAX =  100000;
int i, j, v, num, color[MAX];
vector<int> list[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(i=0; i<list[u].size(); i++){
     v = list[u][i];
     if(color[v] == -1){
       color[v] = c;
       S.push(v);
     }
   }
 }
}
  
void assigncolor(){
 int id = 1;
 for(i=0; i<num; i++){
   color[i] = -1;
 }
 for(j=0; j<num; j++){
   if(color[j] == -1)
     dfs(j, id++);
 }
}
  
int main(){
 int a, b, trial, start, goal, kaisuu;
 cin >> num >>kaisuu;
  
 for(i=0; i<kaisuu; i++){
   cin >> a >> b;
   list[a].push_back(b);
   list[b].push_back(a);
 }
 
 assigncolor();
 
 cin >> trial;
 
 for(i=1; i<=trial; i++){
   cin >> start >> goal;
   if(color[start] == color[goal]){  
     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;
}

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

#define INPUT_FROM_FILE (0) 
#if INPUT_FROM_FILE
#include <fstream>
#endif

void bfs(std::vector<std::vector<int> > &G, std::vector<int> &component_number, int i, int c){
	std::queue<int> que;

	que.push(i);
	component_number[i] = c;
	while(!que.empty()){
		int n = que.front(); que.pop();
		
		for(int j = 0; j < G[n].size(); j++){
			int nn = G[n][j];
			if(component_number[nn] < 0){
				component_number[nn] = c;
				que.push(nn);
			}
		}
	}
	return;
}


int main(int argc, char **argv){
	int n, m, u, v, q, s, t;
	std::vector<std::vector<int> > G;
	std::vector<int> component_number;
	int c = 0;

#if INPUT_FROM_FILE
	std::ifstream ifs("test.txt");
	//FILE *fp = fopen("test.txt", "r");
#endif

#if INPUT_FROM_FILE
	ifs >> n >> m;
#else
	std::cin >> n >> m;
#endif

	G.resize(n);
	component_number.resize(n, -1);
	for(int i = 0; i < m; i++){
#if INPUT_FROM_FILE
		ifs >> u >> v;
#else
		std::cin >> u >> v;
#endif
		G[u].push_back(v);
		G[v].push_back(u);
	}

	for(int i = 0; i < n; i++){
		if(component_number[i] < 0){
			bfs(G, component_number, i, c);
			c++;
		}
	}

#if INPUT_FROM_FILE
	ifs >> q;
#else
	std::cin >> q;
#endif
	for(int i = 0; i < q; i++){
#if INPUT_FROM_FILE
		ifs >> s >> t;
#else
		std::cin >> s >> t;
#endif
		if(component_number[s] == component_number[t]){
			std::cout << "yes" << std::endl;
		}
		else{
			std::cout << "no" << std::endl;
		}
	}
	return 0;
}