Go: package main

import (
	"bufio"
	"fmt"
	"log"
	"os"
	"strconv"
	"strings"
)

// Node 頂点
type Node struct {
	gid  int   // グループID
	edge []int // 隣接辺
}

// NoID グループIDなし
const NoID = -1

// NewNode 頂点の生成
func NewNode() *Node {
	return &Node{gid: NoID, edge: []int{}}
}

func parseNode(nodes []*Node, gid int, queue []int) {
	if len(queue) == 0 {
		return
	}
	var nextQ []int
	for _, id := range queue {
		node := nodes[id]
		if node.gid == NoID {
			node.gid = gid
			for _, edge := range node.edge {
				nextQ = append(nextQ, edge)
			}
		}
	}
	parseNode(nodes, gid, nextQ)
	return
}
func digNode(nodes []*Node, id, gid int) {
	node := nodes[id]
	if node.gid != NoID {
		// 探索済み
		return
	}
	node.gid = gid
	for _, edge := range node.edge {
		digNode(nodes, edge, gid)
	}
	return
}

func main() {
	scanner := bufio.NewScanner(os.Stdin)
	n, m := eGetInt2(scanner)

	nodes := make([]*Node, n)
	for i := 0; i < n; i++ {
		nodes[i] = NewNode()
	}

	for i := 0; i < m; i++ {
		a, b := eGetInt2(scanner)
		nodes[a].edge = append(nodes[a].edge, b)
		nodes[b].edge = append(nodes[b].edge, a)
	}

	for i := 0; i < n; i++ {
		// 幅優先探索
		// gid := i
		// queue := []int{i}
		// parseNode(nodes, gid, queue)

		// 深さ優先探索
		digNode(nodes, i, i)
	}

	q := eGetInt(scanner)
	for i := 0; i < q; i++ {
		a, b := eGetInt2(scanner)
		if nodes[a].gid == nodes[b].gid {
			fmt.Println("yes")
		} else {
			fmt.Println("no")
		}
	}
}

func eGetInt(scanner *bufio.Scanner) int {
	t := eAtoi(strings.Fields(eGetline(scanner)))
	return t[0]
}
func eGetInt2(scanner *bufio.Scanner) (int, int) {
	t := eAtoi(strings.Fields(eGetline(scanner)))
	return t[0], t[1]
}

func eGetline(p *bufio.Scanner) string {
	if !p.Scan() {
		if err := p.Err(); err != nil {
			log.Fatal(err.Error())
		}
		return ""
	}
	return p.Text()
}

func eAtoi(s []string) []int {
	ints := make([]int, len(s))
	var err error
	for i, e := range s {
		ints[i], err = strconv.Atoi(e)
		if err != nil {
			log.Fatal(err.Error())
		}
	}
	return ints
}

C++: #include<stdio.h>
#include<vector>
#include<string>
#include<iostream>
using namespace std;

vector<vector<int> >g;
int n,m,q,s,t;

vector<bool>visited;
vector<int>color;
void dfs(int s){
    for(int i=0;i<g[s].size();i++){
        if(color[g[s][i]]==-1){
            color[g[s][i]]=color[s];
            dfs(g[s][i]);
        }
    }
}
bool dfs2(int s,int t){
    if(s==t)return true;
    visited[s]=true;
    for(int i=0;i<g[s].size();i++){
        if(!visited[g[s][i]]){
            if(dfs2(g[s][i],t)){
                return true;
            }
        }
    }
    return false;
}
int main() {
    scanf("%d %d",&n,&m);
    g.resize(n);
    color.resize(n,-1);
    for(int i=0;i<m;i++){
        scanf("%d %d",&s,&t);
        g[s].push_back(t);
        g[t].push_back(s);
    }
    for(int i=0;i<n;i++){
        if(color[i]==-1){
            color[i]=i;
            dfs(i);
        }
    }
    scanf("%d",&q);
    for(int i=0;i<q;i++){
        scanf("%d %d",&s,&t);
        for(int j=0;j<n;j++)visited[j]=false;
        string s1=(dfs2(s,t)?"yes":"no");
        string s2=(color[s]==color[t]?"yes":"no");
        //if(s1!=s2&&s1=="yes")return 1;
        cout<<s1<<endl;
    }
    return 0;
}

C++: #include<stdio.h>
using namespace std;

const int MAX = 100000;

int parent(int table[], int child) {
	while (table[child] != -1) {
		child = table[child];
	}
	return child;
}

int main() {
	int n, m, q;
	int table[MAX];

	scanf("%d %d", &n, &m);

	for (int i = 0; i < n; i++)table[i] = -1;
	for (int i = 0; i < m; i++) {
		int s, t;
		scanf("%d %d", &s, &t);
		
		int ps = parent(table, s);
		int pt = parent(table, t);
		if (ps != pt) {
			table[ps] = pt;
		}
	}

	scanf("%d", &q);

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

		int ps = parent(table, s);
		int pt = parent(table, t);

		if (ps == pt) {
			printf("yes\n");
		}
		else {
			printf("no\n");
		}
	}
	return 0;
}

C++: #include <stdio.h>
#include <iostream>
#include <list>
using namespace std;

class Node
{
private:
public:
	Node();
	int id;
	list<int> next_node_list;
	int next_idx;
	void AddNextNode(int id);
	void SetGroup(int prev_id, int num);
	int group;
	void Init(int id);
};

Node::Node()
{
	group = 0;
	next_idx = 0;
}

void Node::AddNextNode(int id)
{
	next_node_list.push_back(id);
}

Node *Node_list;

void Node::SetGroup(int prev_id, int num)
{
	group = num;

	list<int>::iterator itr;
	itr = next_node_list.begin();
	for (int i = 0; i < next_idx; i++) {
		itr++;
	}
	
	for(; itr != next_node_list.end(); itr++){
		next_idx++;
		if (prev_id != *itr) {
			Node_list[*itr].SetGroup(id, num);
		}
	}
}

void Node::Init(int id)
{
	this->id = id;
}

int main(void)
{
	//input
	int n;
	cin >> n;
	Node_list = new Node[n]();
	for (int i = 0; i < n; i++) {
		Node_list[i].Init(i);
	}
	int m;
	cin >> m;
	for (int i = 0; i < m; i++) {
		int s, t;
		cin >> s >> t;
		Node_list[s].AddNextNode(t);
		Node_list[t].AddNextNode(s);
	}

	//group
	int group = 1;
	for (int i = 0; i < n; i++) {
		if (Node_list[i].group) continue;
		Node_list[i].SetGroup(-1, group);
		group++;
	}
	
	//output
	int q;
	cin >> q;
	for (int i = 0; i < q; i++) {
		int s, t;
		cin >> s >> t;
		if (Node_list[s].group == Node_list[t].group && Node_list[s].group != 0) {
			cout << "yes" << "\n";
		}
		else {
			cout << "no" << "\n";
		}
	}
	
	return 0;
}

C++: #include <iostream>
#include <stack>
#include <queue>
#include <vector>
using namespace std;
#define N 100
#define MAX 100000
#define NIL -1
#define rep(i, n) for(int i = 0; i < (n); ++i)

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

void dfs_visits(int r, int id){
    stack<int> S;
    S.push(r);
    color[r] = id;
    while(!S.empty()){
        int u = S.top(); S.pop();
        rep(j, G[u].size()){
            int v = G[u][j];
            if(color[v] == NIL) {
                color[v] = id;
                S.push(v);
            }
        }
    }
}

void dfs(){
    // initialization
    rep(i, n) color[i] = NIL;
    int id = 1;
    rep(u, n){
        if (color[u] == NIL) dfs_visits(u, id++);
    }
}

int main()
{
    int s, t, m, q;
    cin >> n >> m;
    rep(i, m){
        cin >> s >> t;
        G[s].push_back(t);
        G[t].push_back(s);
    }

    dfs();
    
    cin >> q;
    vector<string> ans(q);

    rep(i, q){
        cin >> s >> t;
        if(color[s] == color[t]) ans[i] = "yes";
        else ans[i] = "no";
    }

    rep(i, q){
        cout << ans[i] << endl;
    }

    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;
    }
  }
};