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>
using namespace std;

struct node {
    int to;
    node *next;
};

node *adj[100000], fm[200000];
int g[100000];

int main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);
    int n, m, i;
    cin>>n>>m;
    m+=m;
    int s, t;
    i=0;
    while(i<m) {
        cin>>s>>t;
        fm[i].to=t;
        fm[i].next=adj[s];
        adj[s]=&fm[i];
        i++;
        fm[i].to=s;
        fm[i].next=adj[t];
        adj[t]=&fm[i];
        i++;
    }
    int group=1;
    vector<int> st;
    st.reserve(n);
    for(i=0; i<n; i++) {
        if(g[i]) continue;
        g[i]=group;
        st.push_back(i);
        while(!st.empty()) {
            node *p=adj[st.back()];
            g[st.back()]=group;
            st.pop_back();
            while(p) {
                if(g[p->to]==0) st.push_back(p->to);
                p=p->next;
            }
        }
        group++;
    }
    cin>>n;
    for(int i=0; i<n; i++) {
        cin>>s>>t;
        if(g[s]==g[t]) cout<<"yes\n";
        else cout<<"no\n";
    }
    return 0;
}

C++: #define _USE_MATH_DEFINES

#include <cstdio>
#include <cstdlib>
#include <iostream>
#include <cmath>
#include <algorithm>
#include <vector>
#include <queue>
#include <map>
#include <list>

long long int INF = 1e18;
using namespace std;

typedef pair<long long int, long long int> P;

#define MAX_N 200000

int par[MAX_N];
int rnk[MAX_N];

// 初期化
void init(int n){
	for(int i = 0; i < n; i++){
		par[i] = i;
		rnk[i] = 0;
	}
}

// x の親を返す
int find(int x){
	if(par[x] == x){
		return x;
	}
	return par[x] = find(par[x]);
}

// x と y を併合する
void unite(int x, int y){
	int x_par = find(x);
	int y_par = find(y);
	if(x_par == y_par){
		return;
	}
	
	if(rnk[x_par] < rnk[y_par]){
		par[x_par] = y_par;
	}else{
		par[y_par] = x_par;
		if(rnk[x_par] == rnk[y_par]){
			rnk[x_par]++;
		}
	}
}

// x, y が同じグループか判定
bool same(int x, int y){
	return (find(x) == find(y));
}

int main(){
	
	int n, m;
	cin >> n >> m;
	
	init(n);
	
	for(int i = 0; i < m; i++){
		int x, y;
		cin >> x >> y;
		unite(x, y);
	}
	
	int q;
	cin >> q;
	
	for(int i = 0; i < q; i++){
		int x, y;
		cin >> x >> y;
		if(same(x, y)){
			cout << "yes" << endl;
		}else{
			cout << "no" << endl;
		}
	}
	
	return 0;
}

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

using namespace std;
using Relations = vector<vector<int>>;

const int no_group = -1;
const int no_user_id = -1;

void depth_first_search(Relations& list_graph, int started_user_id, vector<int>& connected_group, int group_id) {
  stack<int> visited_path;
  visited_path.push(started_user_id);
  connected_group[started_user_id] = group_id;

  while(!visited_path.empty()) {
    int current_user_id = visited_path.top();

    int unvisited_adjacency_user_id = no_user_id;
    for(int i = 0; i < list_graph[current_user_id].size(); i++) {
      int adjacency_user_id = list_graph[current_user_id][i];
      if(connected_group[adjacency_user_id] == no_group) {
        unvisited_adjacency_user_id = adjacency_user_id;
        break;
      }
    }

    if(unvisited_adjacency_user_id != no_user_id) {
      connected_group[unvisited_adjacency_user_id] = group_id;
      visited_path.push(unvisited_adjacency_user_id);
    } else {
      visited_path.pop();
    }
  }
}


int main() {
  int user_num;
  int relation_num;
  Relations list_graph;

  // Init
  cin >> user_num >> relation_num;
  list_graph.resize(user_num);

  // Construct list graph
  for(int i = 0; i < relation_num; i++) {
    int user1_id, user2_id;
    cin >> user1_id >> user2_id;
    list_graph[user1_id].push_back(user2_id);
    list_graph[user2_id].push_back(user1_id);
  }

  // Group connected component
  vector<int> connected_group(user_num, no_group);

  int group_id = 0;
  for(int i =  0; i < user_num; i++) {
    if(connected_group[i] == no_group) {
      depth_first_search(list_graph, i, connected_group, group_id++);
    }
  }


  // Answer queries
  int query_num;
  cin >> query_num;
  for(int i = 0; i < query_num; i++) {
    int user1_id, user2_id;
    cin >> user1_id >> user2_id;

    if(connected_group[user1_id] == connected_group[user2_id]) {
      cout << "yes";
    } else {
      cout << "no";
    }
    cout << endl;
  }
}

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

using namespace std;

static const int MAX = 100000;

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

void dfs (int r, int c) {

    int i, u, v;

    stack<int> S;
    S.push(r);
    color[r] = c;

    while (!S.empty()) {
        u = S.top();
        S.pop();
        for (i = 0; i < G[u].size(); i++) {
            v = G[u][i];
            if (color[v] == -1) {
                color[v] = c;
                S.push(v);
            }
        }
    }

}

void assignColor () {

    int id = 1, i, u;

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

}

int main () { 

    int s, t, m, q, i;

    cin >> n >> m;

    for (i = 0; i < m; i++) {
        cin >> s >> t;
        G[s].push_back(t);
        G[t].push_back(s);
    }

    assignColor ();

    cin >> q;

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

    return 0;

}

C++: #include<cstdio>
#include<queue>

using namespace std;

static const int N = 100000;

int m,n;

queue<int> Q[N];
int color[N];

void visit(int a,int c){
    color[a] = c;
   while( !(Q[a].size() == 0) ){
        int u = Q[a].front();
        if(color[u] == 0) visit(u,c);
        Q[a].pop();
    }
}

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

    for(int i=0; i<n; i++) color[i] = 0;

    for(int i=0; i<m;i++){
        int u,v;
        scanf("%d",&u);
        scanf("%d",&v);
        Q[u].push(v);
        Q[v].push(u);
    }
    
    int cc = 1;

    for(int i=0; i<n; i++){
        if(color[i] == 0){
            visit(i,cc);
            cc++;
        }
    }

    int l; 
    scanf("%d",&l);
    for(int i =0 ;i<l;i++){
        int x,y;
        scanf("%d",&x);
        scanf("%d",&y);

        if(color[x] == color[y]) printf("yes\n");
        else printf("no\n");

    }

}