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<iostream>
#include<vector>
#include<stack>
using namespace std;
vector<int>v[100000];
int color[100000];
void dpf(int a,int c) {
    color[a] = c;
	stack<int>s;
	for (int i = 0; i < v[a].size(); i++) {
		int t = v[a][i];
		s.push(t);
		color[t] = c;
	}
	while (!s.empty())
	{
		int k = s.top();
		s.pop();
		for (int i = 0; i < v[k].size(); i++) {
			
			int t = v[k][i];
			if (color[t] == 0) {
				s.push(t);
				color[t] = c;
			}
		}
	}
}
void setcolor(int n) {
	int t=1;
	for (int i = 0; i < n; i++) {
		if (color[i] == 0) {
			dpf(i, t++);
		}
	}
}
int main(void) {
	int n,k;
	cin >> n;
	cin >> k;
	for (int i = 0; i < k; i++) {
		int a, b;
		cin >> a >> b;
		v[a].push_back(b);
		v[b].push_back(a);
	}
	setcolor(n);
	int q;
	cin >> q;
	for (int i = 0; i < q; i++) {
		int a, b;
		cin >> a >> b;
		if (color[a]==color[b])
		{
			cout << "yes";
		}
		else {
			cout << "no";
		}
		cout << endl;
	}
}

C++: #include<iostream>
#include<vector>
using namespace std;
vector<vector<int>> G(100);
vector<int> c(100);
void dfs(int s, int x){
    if(c[s]) return;
    c[s]=x;
    for(auto a:G[s]) dfs(a,x);
}
int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    int n,m;
    cin>>n>>m;
    for(int i=0;i<m;++i){
        int a,b;
        cin>>a>>b;
        G[a].push_back(b);
        G[b].push_back(a);
    }
    for(int i=0;i<n;++i) dfs(i,i+1);
    int q;
    cin>>q;
    for(int i=0;i<q;++i){
        int a,b;
        cin>>a>>b;
        cout<<(c[a]-c[b]?"no":"yes")<<endl;
    }
}

C++: #include <iostream>
#include <queue>
#include <cstdio>
#include <vector>
using namespace std;
#define MAX_N 100000
int n;

bool can_connect(int s,int t,const vector< vector<int> > &g) {
  bool visited[n];
  queue<int> que;
  for(int i=0;i<n;i++) visited[i] = false;
  while(!que.empty()) que.pop();

  visited[s] = true;
  que.push(s);
  while(!que.empty()) {
    int v = que.front(); que.pop();
    for(int i=0;i<g[v].size();i++) {
      if(!visited[g[v][i]]) {
        if(g[v][i] == t) return true;
        visited[g[v][i]] = true;
        que.push(g[v][i]);
      }
    }
  }
  return false;
}

int main() {
  int m,s,t,q;
  scanf("%d %d\n",&n,&m);
  vector< vector<int> > g(n);
  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<g.size();i++) {
    printf("%d : ",i);
    for(int j=0;j<g[i].size();j++) {
      printf("%d ",g[i][j]);
    }
    printf("\n");
  }
  */

  scanf("%d",&q);
  for(int i=0;i<q;i++) {
    scanf("%d %d",&s,&t);
    //printf("%d,%d: ",s,t);
    if(can_connect(s,t,g)){
      printf("yes\n");
    }
    else {
      printf("no\n");
    }
  }
}

C++: #include <cstdio>
#include <algorithm>
#include <unordered_map>
#include <vector>
int main(){
    int n;
    int m;
    std::scanf("%d", &n);
    std::scanf("%d", &m);

    std::unordered_map<int, int> map;
    for(int i = 0; i < m; ++i){
        int s;
        int t;
        std::scanf("%d", &s);
        std::scanf("%d", &t);
        if(map.find(s) == map.end() && map.find(t) == map.end()){
            int small = std::min(s, t);
            int large = std::max(s, t);
            map.insert(std::make_pair(small, small));
            map.insert(std::make_pair(large, small));
        } else if(map.find(s) == map.end()){
            int key = map[t];
            while(key != map[key]){
                key = map[key];
            }
            if(key <= s){
                map.insert(std::make_pair(s, key));
            } else {
                map[key] = s;
                map.insert(std::make_pair(s, s));
            }
        } else if(map.find(t) == map.end()){
            int key = map[s];
            while(key != map[key]){
                key = map[key];
            }
            if(key <= t){
                map.insert(std::make_pair(t, key));
            } else {
                map[key] = t;
                map.insert(std::make_pair(t, t));
            }
        } else {
            int keys = map[s];
            while(keys != map[keys]){
                keys = map[keys];
            }
            int keyt = map[t];
            while(keyt != map[keyt]){
                keyt = map[keyt];
            }
            int small = std::min(keys, keyt);
            int large = std::max(keys, keyt);
            map[large] = small;
        }
    }

    int q;
    std::scanf("%d", &q);
    for(int i = 0; i < q; ++i){
        int s;
        int t;
        std::scanf("%d", &s);
        std::scanf("%d", &t);
        if(map.find(s) == map.end() || map.find(t) == map.end()){
            printf("no\n");
            continue;
        }
        int keys = map[s];
        while(keys != map[keys]){
            keys = map[keys];
        }
        int keyt = map[t];
        while(keyt != map[keyt]){
            keyt = map[keyt];
        }
        if(keys == keyt){
            std::printf("yes\n");
        } else {
            std::printf("no\n");
        }
    }

    return 0;
}

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