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 <bits/stdc++.h>
using namespace std;
#define MAX 100005

vector<vector<int> > G, R;
vector<int> ve;
queue<int> Q;
int choose[MAX];
int n, m, i, j;

int main(void) {
	cin >> n >> m;
	G.resize(n);
	int a, b;
	for (i = 0; i < m; i++) {
		cin >> a >> b;
		G[a].push_back(b);
		G[b].push_back(a);
	}
	for (i = 0; i < n; i++) {
		choose[i] = 0;
	}
	for (i = 0; i < n; i++) {
		if (choose[i] != 0)
			continue;
		Q.push(i);
		ve.clear();
		ve.push_back(i);
		choose[i] = 1;
		int now, cnt, next;
		while (!Q.empty()) {
			now = Q.front();
			Q.pop();
			for (cnt = 0; cnt < G[now].size(); cnt++) {
				next = G[now][cnt];
				if (choose[next] == 0) {
					Q.push(next);
					ve.push_back(next);
					choose[next] = 1;
				}
			}
		}
		R.push_back(ve);
		int dis = R.size() - 1;
		sort(R[dis].begin(), R[dis].end());
	}
	cin >> m;
	for (i = 0; i < m; i++) {
		cin >> a >> b;
		for (j = 0; j < R.size(); j++) {
			if (*(lower_bound(R[j].begin(), R[j].end(), a)) == a) {
				if (*(lower_bound(R[j].begin(), R[j].end(), b)) == b) 
					cout << "yes" << endl;
				else
					cout << "no" << endl;
			}
		}
	}
}

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

using namespace std;
queue<int>q;
vector<int>E[100005];
int d[100005],v[100005],n;
int id;
void bfs(int s,int id)
{
    d[s]=id;
    v[s]=true;
    q.push(s);
    while(!q.empty())
    {
        int u=q.front();q.pop();
        for(auto i:E[u])
        {
            if(!v[i])
            {
                v[i]=true;
                d[i]=id;
                q.push(i);
            }
        }
    }
}
int main()
{
    int m;
    cin>>n>>m;
    for(int i=0;i<m;i++)
    {
        int s,t;
        cin>>s>>t;
        E[s].push_back(t);
        E[t].push_back(s);
    }
    int q;cin>>q;
    id=1;
    for(int i=1;i<=n;i++)d[i]=-1;
    for(int i=1;i<=n;i++)
        if(d[i]==-1)
        bfs(i,id++);
    for(int i=0;i<q;i++)
    {
        int s,t;
        cin>>s>>t;
        if(d[s]==d[t])cout<<"yes"<<endl;
        else cout<<"no"<<endl;
    }
    return 0;
}

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

using namespace std;

// int d[10010];
int n, m;
vector<int> G[100010];
int reached[100010];
int color[100010];
int color_id = 0;

void bfs(int s, int color_id) {
  // cout << "--------------" << endl;
  // cout << "s:" << s << ", color:" << color_id <<endl;
  queue<int> Q;
  Q.push(s);
  while(!Q.empty()) {
    int u = Q.front(); Q.pop();
    // cout << "G[u].size():" << G[u].size() << endl;
    for (int i = 0; i < G[u].size(); i++) {
      // cout << u << "->" << G[u][i] << endl;
      if (reached[G[u][i]] == -1) {
        // cout << "reached at:" << G[u][i] << endl;
        Q.push(G[u][i]);
        reached[G[u][i]] = 1;
        color[G[u][i]] = color_id;
      }
    }
  }
}

void assignColor() {
  for (int i = 0; i < n; i++) {
    color[i] = -1;
  }

  for (int i = 0; i < n; i++) {
    if (color[i] == -1) {
      for (int j = 0; j < n; j++) {
        reached[j] = -1;
      }
      bfs(i, ++color_id);
    }
  }
}

int main() {
  cin >> n >> m;
  int s, t;

  // 初期化
  for (int i = 0; i < m; i++) {
    cin >> s >> t;
    G[s].push_back(t);
    G[t].push_back(s);
  }
  // お絵かき
  assignColor();

  // 質問
  int q;
  cin >> q;
  // cout << "number of question:" << q << endl;
  for (int i = 0; i < q; i++) {
    cin >> s >> t;
    if (color[s] == -1 || color[t] == -1) {
      cout << "no" << endl;
    } else {
      if (color[s] == color[t]) {
        cout << "yes" << endl;
      } else {
        cout << "no" << endl;
      }
    }
  }
  // お絵かきの確認
  // cout << "----------" << endl;
  //
  // for (int i = 0; i < n; i++) {
  //   cout << i << ": " << color[i] << endl;
  // }

}

C++: #include<bits/stdc++.h>

using namespace std;

#define yes             cout << "yes\n"
#define no              cout << "no\n"
#define lop(n)          for(int i = 0; i < n; i++)
#define N               100009

int rep[N], n, m;

int findrep(int a)
{
    if(rep[a] == a)
        return a;

    return rep[a] = findrep(rep[a]);
}

void Union(int a, int b)
{
    rep[findrep(a)] = findrep(b);
}

int main()
{
    int u, v, q;

    cin >> n >> m;

    lop(n) rep[i] = i;

    lop(m)
    {
        cin >> u >> v;

        Union(u, v);
    }

    lop(n) u = findrep(i);

    cin >> q;

    lop(q)
    {
        cin >> u >> v;

        rep[u] == rep[v] ? yes : no;
    }

    return 0;
}

C++: #include <iostream>
#include <vector>
#include <stack>
using namespace std;
typedef long long ll;
static const ll MAX = 110000;
static const ll NIL = -1;

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

void dfs(ll r, ll c) {
  stack<ll> S;
  S.push(r);
  color[r] = c;
  while (!S.empty()) {
    ll u = S.top(); S.pop();
    for (ll i = 0; i < G[u].size(); i++) {
      ll v = G[u][i];
      if (color[v] == NIL) {
        color[v] = c;
        S.push(v);
      }
    }
  }
}

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

int main() {
  ll s, t, m, q;
  cin >> n >> m;
  for (ll i = 0; i < m; i++) {
    cin >> s >> t;
    G[s].push_back(t);
    G[t].push_back(s);
  }

  assignColor();

  cin >> q;

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

  return 0;
}