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;
struct cww{cww(){ios::sync_with_stdio(false);cin.tie(0);}}star;
#define P(x) cout << (x) << endl
#define p(x) cout << (x)
#define all(c) (c).begin(), (c).end()
#define rall(c) (c).rbegin(), (c).rend()
#define vv(type, c, m, n, i) vector<vector<type>> c(m, vector<type>(n, i));
#define rep(i,a,n) for(int i=(a), i##_len=(n); i<i##_len; ++i)
#define rrep(i,a,n) for(int i=(a), i##_len=(n); i>i##_len; --i)
#define len(x) ((int)(x).size())
#define mp make_pair
#define eb emplace_back
typedef long long ll;
typedef vector<int> vi;
typedef vector<double> vd;
typedef vector<long long> vll;
typedef vector<string> vs;
typedef vector<bool> vb;
vi G;
inline int root(int x){ return G[x] < 0 ? x : G[x] = root(G[x]); }
inline void uniteSet(int x, int y){
    x = root(x);
    y = root(y);
    if (x == y) return;
    if (G[x] > G[y]) swap(x, y);
    G[y] = x;
}
inline bool findSet(int x, int y){
	if((x != -1 && y != -1) && (G[x] == G[y])) return true;
	return root(x) == root(y);
}
int main() {
	int n, m; cin >> n >> m;
	G.resize(n, -1);
	int s, t;
	rep(i, 0, m) {
		cin >> s >> t;
		uniteSet(s, t);
	}
	int q; cin >> q;
	rep(i, 0, q) {
		cin >> s >> t;
		P(findSet(s, t) ? "yes" : "no");
	}
	return 0;
}

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

#define MAX 100000

#define WHITE 0
#define GRAY 1
#define BLACK 2


using namespace std;

vector<int> G[MAX];
int graphc[MAX];
int color[MAX];
int colorCount;

void def(int o)
{
	int v;

	for (int i = 0; i < G[o].size(); i++) {

		v = G[o][i];
		if (color[v] == WHITE) {

			color[v] = GRAY;
			def(v);
		}
	}
	color[o] = BLACK;
	graphc[o] = colorCount;
}


int main(void)
{
	int n;
	int m;
	int s;
	int t;
	int q;


	cin >> n >> m;

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

	for (int i = 0; i < n; i++) {

		if (color[i] == WHITE) {
			colorCount++;
			def(i);
			
		}
	}



	cin >> q;

	for (int i = 0; i < q; i++) {

		cin >> s >> t;

		cout << ((graphc[s] == graphc[t]) ? "yes" : "no" )<< endl;
	}

	return 0;
}

C++: #include<cstdio>
#include<vector>
#include<cstring>
#include<stack>
#include<iostream>
using namespace std;
int visited[100000]; int n;
vector<int> G[100000];

//void dfs_visit(int u)
//{
//  if(visited[u] == 1) return;
//  visited[u] = 1;
//  for(int i=0; i<G[u].size(); i++)
//  {
//    int v = G[u][i];
//    if(visited[v] == 0)
//      dfs_visit(v);
//  }
//}
//void dfs(int u, int v)
//{
//  memset(visited, 0, sizeof(n)*n);
//  dfs_visit(u);
//  if(visited[u] == visited[v])
//    printf("yes\n");
//  else printf("no\n");
//}  果然超时了哦。属实是弟弟行为哦~不过好歹能用哈哈哈。
void dfs_visit(int u, int id)
{
  if(visited[u] != 0) return;
  visited[u] = id;
  stack<int> s;//  诶~有意思。用stack来实现DFS一次把下层节点全压栈与一次压下层的一个节点仅仅是子节点的访问顺序颠倒了。
  s.push(u);
  while(!s.empty())
  {
    int v = s.top(); s.pop();
    for(int i=0; i<G[v].size(); i++)
    {
      int x = G[v][i];
      if(visited[x] == 0)
      {
        s.push(x);
        visited[x] = id;
      }
    }
  }
}
void dfs(int u)
{
  memset(visited, 0, sizeof(n)*n);
  int id = 1;// use id to denotes different circle so that all nodes can be visited by one bfs.
  for(int i=0; i<n; i++)
  {
    if(visited[i] == 0)
      dfs_visit(i, id++); // first circle id = 1, then 2 and so on ...
  }
}

int main()
{
  int m, q, u, v;
  scanf("%d%d",&n, &m);
  for(int i=0; i<m; i++)
  {
    scanf("%d%d", &u, &v);
    G[u].push_back(v);
    G[v].push_back(u);
  }
  scanf("%d", &q);
  dfs(0);
  for(int i=0; i<q; i++)
  {
    scanf("%d%d", &u, &v);
    if(visited[u] == visited[v])  printf("yes\n");
    else printf("no\n");
  }


  return 0;
}

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

using namespace std;

const int WHITE = 0, GREY = 1, BLACK = 2;

struct CC {
    int n;
    vector<vector<int>> g;
    vector<int> color;
    vector<int> component;
    int cId = 0; //component id
    
    CC (int n) : n(n) {
        g.assign(n, vector<int>(0));
        color.assign(n, WHITE);
        component.assign(n, -1);
    }
    
    void addEdge (int u, int v) {
        g[u].push_back(v);
        g[v].push_back(u);
    }
    
    void solve () {
        for (int i = 0; i < n; i++) {
            if (color[i] == WHITE) {
                cId++;
                bfs(i);
            }
        }
    }
    
    void bfs (int s) {
        queue<int> q;
        q.push(s);
        color[s] = GREY;
        component[s] = cId;
        while (!q.empty()) {
            int u = q.front();
            q.pop();
            for (int v : g[u]) {
                if (color[v] == WHITE) {
                    q.push(v);
                    color[v] = GREY;
                    component[v] = cId;
                }
            }
        }
    }
};

int main() {
    
    int n, m;
    cin >> n >> m;
    CC cc(n);
    
    for (int i = 0; i < m; i++) {
        int u, v;
        cin >> u >> v;
        cc.addEdge(u, v);
    }
    
    cc.solve();
    
    int q;
    cin >> q;
    for (int i = 0; i < q; i++) {
        int u, v;
        cin >> u >> v;
        if (cc.component[u] == cc.component[v]) {
            cout << "yes" << endl;
        }
        else {
            cout << "no" << endl;
        }
    }
    
    return 0;
}