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 <string>
#include <vector>
#include <queue>
#include <algorithm>
#include <unordered_set>

using namespace std;

template<typename ISTREAM>
void readGraphListFromFriendInfo(ISTREAM& cin, vector< vector<int> >& friendGraphList) {
	size_t n;
	cin >> n;
	friendGraphList = vector< vector<int> >(n);
	size_t m;
	cin >> m;
	for (size_t i = 0; i != m; ++i) {
		size_t s,t;
		cin >> s >> t;
		friendGraphList.at(s).push_back(t);
		friendGraphList.at(t).push_back(s);
	}
	for (auto& v : friendGraphList)v.shrink_to_fit();
}

void accesibleNodeSearch(const vector<vector<int>>& graphList, vector<vector<bool>>& visitMatrix, const int s) {
	const size_t n = graphList.size();
	queue<int> nodeQueue;
	vector<bool>& visitList = visitMatrix.at(s);
	visitList.resize(n, false);
	nodeQueue.push(s);
	visitList.at(s).flip();
	while (!nodeQueue.empty()) {
		const int id = nodeQueue.front();
		const vector<int>& adjList = graphList.at(id);
		for (const auto& adjID : adjList) {
			if (visitList.at(adjID))continue;
			const vector<int>& idList = graphList.at(adjID);
			if (find(idList.begin(), idList.end(), id) == idList.end())continue;
			nodeQueue.push(adjID);
			visitList.at(adjID).flip();
		}
		nodeQueue.pop();
	}
}

void buildFriendAccesibility(const vector<vector<int>>& graphList, vector<vector<bool>>& visitMatrix) {
	const int n = graphList.size();
	visitMatrix.resize(n, vector<bool>(n, false));
	for (int i = 0; i != n; ++i) {
		accesibleNodeSearch(graphList, visitMatrix, i);
	}
}

template<typename T>
void execute(T& cin) {
	vector< vector<int> > graphList;
	readGraphListFromFriendInfo(cin, graphList);
	vector<vector<bool>> visitMatrix;
	buildFriendAccesibility(graphList, visitMatrix);
	int q, s, t;
	cin >> q;
	for (int i = 0; i != q; ++i) {
		cin >> s >> t;
		cout << (visitMatrix.at(s).at(t) ? "yes" : "no") << endl;
	}
}

int main()
{


	execute(cin);


	return 0;
}

C++: #include <iostream>
#include <cstdio>
#include <vector>
#include <algorithm>
#include <map>
#include <numeric>
#include <string>
#include <cmath>
#include <iomanip>
#include <string>
#include <queue>
#include <list>
#include <stack>

using namespace std;

/* constant */

const int INF = 1 << 30;
const int mod = 1000000007;
const int MAX_N = 100000;

/* typedef */

typedef long long ll;

/* global variables */

vector< vector<int> > Adj(MAX_N, vector<int>());
vector<int> link(MAX_N, -1);
int n;

/* function */
void bfs(int start);

/* main */
int main() {

    int m; cin >> n >> m;
    for (int i = 0; i < m; i++) {
        int u, v; cin >> u >> v;
        Adj[u].push_back(v);
        Adj[v].push_back(u);
    }

    for (int i = 0; i < n; i++) {
        if (link[i] == -1) {
            bfs(i);
        }
    }

    int q; cin >> q;
    for (int i = 0; i < q; i++) {
        int u, v; cin >> u >> v;
        if (link[u] == link[v]) {
            cout << "yes" << '\n';
        }
        else {
            cout << "no" << '\n';
        }
    }
}

void bfs(int start) {
    
    link[start] = start;
    queue<int> q;
    q.push(start);

    while (!q.empty()) {

        int cur = q.front(); q.pop();

        for (auto v : Adj[cur]) {

            if (link[v] == -1) {
                link[v] = start;
                q.push(v);
            }

        }

    }
}

C++: #include <iostream>
#include <cstdio>
#include <cstdlib>
#include <stack>
#include <vector>
#include <algorithm>
#include <cmath>
#include <climits>
#include <cstring>
#include <queue>
#include <string>

using namespace std;

const double PI = 3.14159265358979;

vector<int> G[100000];
int visited[100000];

void dfs_stack(int node, int color) {

	stack<int> st;

	visited[node] = color;
	st.push(node);

	while (!st.empty()) {

		int u = st.top();
		bool isPop = true;
		for (int i = 0; i < G[u].size(); i++) {
			if (!visited[G[u][i]]) {
				visited[G[u][i]] = color;
				st.push(G[u][i]);
				isPop = false;
			}
		}
		if (isPop) {
			st.pop();
		}
	}
}

int main() {
	
	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++)	{
		if (!visited[i])
			dfs_stack(i, i + 1);
	}

	int q; cin >> q;
	for (int i = 0; i < q; i++) {
		int a, b;
		cin >> a >> b;
		if (visited[a] == visited[b] && visited[a] && visited[b]) {
			cout << "yes" << endl;
		}
		else {
			cout << "no" << endl;
		}
	}

	return 0;
}

C++: #include <iostream>
#include <vector>
#include <algorithm>
#include <queue>
#include <stack>
#include <stdio.h>
#include <cmath>
#include <set>
#include <map>
using namespace std;

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

vector<bool>visited;
bool dfs(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(dfs(g[s][i],t)){
                return true;
            }
        }
    }
    return false;
}
int main() {
    cin>>n>>m;
    g.resize(n);
    for(int i=0;i<m;i++){
        int s,t;
        cin>>s>>t;
        g[s].push_back(t);
        g[t].push_back(s);
    }
    cin>>q;
    for(int i=0;i<q;i++){
        visited.resize(n,false);
        int s,t;
        cin>>s>>t;
        cout<<(dfs(s,t)?"yes":"no")<<endl;
    }
    return 0;
}