Go: package main

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

var scanner = bufio.NewScanner(os.Stdin)

func nextString() string {
	scanner.Scan()
	return scanner.Text()
}

func nextInt() int {
	n, err := strconv.Atoi(nextString())
	if err != nil {
		fmt.Printf("strconv.Atoi failed: %v\n", err)
	}
	return n
}

func newGraph(nNodes int) *Graph {
	g := Graph{}
	g.nodes = make([]*GraphNode, nNodes)
	for iNode := 0; iNode < len(g.nodes); iNode++ {
		g.nodes[iNode] = &GraphNode{}
		g.nodes[iNode].key = GraphNodeKey(iNode)
	}
	return &g
}

var infty = 1000000000

type GraphNodeKey int

// GraphNode is a node for undirected graph
type GraphNode struct {
	key       GraphNodeKey
	adjacents []*GraphNode
	visited   bool
	d, f      int
	parent    *GraphNode
	cc        int
}

func (g *Graph) setAdjacent(l, r GraphNodeKey) {
	g.nodes[l].adjacents = append(g.nodes[l].adjacents, g.nodes[r])
}

// Graph is a undirected graph
type Graph struct {
	nodes []*GraphNode
}

func (g *Graph) initialize() {
	for iNode := 0; iNode < len(g.nodes); iNode++ {
		g.nodes[iNode].visited = false
		g.nodes[iNode].d = infty
		g.nodes[iNode].f = infty
		g.nodes[iNode].parent = nil
		g.nodes[iNode].cc = -1 // 22.3-12
	}
}

type QueueEntry struct {
	node *GraphNode
	next *QueueEntry
}

type Queue struct {
	head, tail *QueueEntry
}

func (q *Queue) enqueue(node *GraphNode) {
	entry := QueueEntry{}
	entry.node = node

	if q.tail == nil {
		q.head = &entry
		q.tail = &entry
		return
	}

	q.tail.next = &entry
	q.tail = q.tail.next
}

func (q *Queue) dequeue() *QueueEntry {
	if q.head == nil {
		return nil
	}
	poped := q.head
	q.head = q.head.next
	if q.head == nil {
		q.tail = nil
	}
	return poped
}

func (q *Queue) isEmpty() bool {
	return q.head == nil
}

var time = 0

func fillDistancesByDepthFirstSearch(g *Graph) {
	g.initialize()
	time = 0
	cc := 0

	for _, u := range g.nodes {
		if !u.visited {
			dfsVisit(g, u, cc)
			cc++
		}
	}
}

func dfsVisit(g *Graph, u *GraphNode, cc int) {
	time++
	u.d = time
	u.cc = cc

	u.visited = true
	for _, v := range u.adjacents {
		if !v.visited {
			v.parent = u
			dfsVisit(g, v, cc)
		}
	}
	time++
	u.f = time
}

func main() {
	scanner.Split(bufio.ScanWords)

	nUsers := nextInt()
	nEdges := nextInt()
	graph := newGraph(nUsers)
	for iEdge := 0; iEdge < nEdges; iEdge++ {
		l := GraphNodeKey(nextInt())
		r := GraphNodeKey(nextInt())
		graph.setAdjacent(l, r)
		graph.setAdjacent(r, l)
	}

	fillDistancesByDepthFirstSearch(graph)

	nQueries := nextInt()
	for iQuery := 0; iQuery < nQueries; iQuery++ {
		l := GraphNodeKey(nextInt())
		r := GraphNodeKey(nextInt())

		// fmt.Println(graph.nodes[l].d, graph.nodes[r].d, graph.nodes[r].f, graph.nodes[l].f)
		if graph.nodes[l].cc == graph.nodes[r].cc {
			fmt.Println("yes")
		} else {
			fmt.Println("no")
		}
	}
}

C++: #include <bits/stdc++.h>
#define rep(i, n) for(int i = 0; i < (n); i++)
using namespace std;
using ll = long long;
using P = pair<int, int>;

void dfs(int id, int gid, vector<vector<int> >& g, int group[]){
	group[id] = gid;
	for(int n : g[id]){
		if(group[n] < 0){
			group[n] = gid;
			dfs(n, gid, g, group);
		}
	}
	return;
}

int main(){
	int n, m; cin >> n >> m;
	int group[n];
	memset(group, -1, n*sizeof(int));
	vector<vector<int> > g(n, vector<int>());
	rep(i, m){
		int s, t; cin >> s >> t;
		g[s].push_back(t);
		g[t].push_back(s);
	}

	int gid = 0;
	rep(i, n) if(group[i] < 0) dfs(i, gid++, g, group);

	int q; cin >> q;
	rep(i, q){
		int s, t; cin >> s >> t;
		cout << ((group[s] == group[t]) ? "yes" : "no") << endl;
	}

	return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;

struct Unionfind {
	vector<int> data;

	Unionfind(int n) { data.assign(n, -1); }

	int root(int n) {
		if (data[n] < 0) return (n);
		return (data[n] = root(data[n]));
	}

	int size(int n) { return (-data[root(n)]); };
	bool same(int x, int y) { return (root(x) == root(y)); }

	void unite(int x, int y) {
		x = root(x), y = root(y);
		if (x == y) return;
		if (data[x] > data[y]) swap(x, y);
		data[x] += data[y];
		data[y] = x;
	}
};

int main() {
    int N, M; cin >> N >> M;
    Unionfind uni(N);
    for (int i = 0; i < M; i++) {
        int a, b; cin >> a >> b;
        uni.unite(a, b);
    }
    int Q; cin >> Q;
    while (Q--) {
        int a, b; cin >> a >> b;
        cout << (uni.same(a, b) ? "yes" : "no") << '\n';
    }
    return (0);
}

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

using namespace std; 

int noc;
vector<int> comp;
vector< vector<int> > adj;

void dfs(int v) {
	comp[v] = noc;
	for (int i = 0; i < adj[v].size(); ++i) {
		if (comp[adj[v][i]] < 0) {
			dfs(adj[v][i]);
		}
	}
	return;
}

int main(void) {
	int nov,noe,u,v;
	cin >> nov >> noe;
	adj = vector< vector<int> >(nov);
	for (int i = 0; i < noe; ++i) {
		cin >> u >> v;
		adj[u].push_back(v);
		adj[v].push_back(u);
	}

	noc = 0;
	comp = vector<int>(nov,-1);
	for (int i = 0; i < nov; ++i) {
		if (comp[i] < 0) {
			++noc;
			dfs(i);
		}
	}

	int noq;
	cin >> noq;
	for (int q = 0; q < noq; ++q) {
		cin >> u >> v;
		if (comp[u] == comp[v]) {
			cout << "yes" << endl;
		}
		else {
			cout << "no" << endl;
		}
	}
	return 0;
}

C++: #include <bits/stdc++.h>
#define ll long long
#define INF 999999999
#define MOD 1000000007

using namespace std;

typedef pair<int,int>P;

const int MAX_N = 100000;

class UnionFind {
private:
    vector<int> par;
public:
    UnionFind(){}
    UnionFind(const int node_size) : par(node_size){
        iota(par.begin(), par.end(), 0);
    }
    int find(int x){
        if(par[x] == x) return x;
        else return par[x] = find(par[x]);
    }
    bool unite(int x, int y){
        int z;
        while(par[x] != par[y]){
            if(par[x] > par[y]) swap(x, y);
            z = par[x], par[x] = par[y];
            if(y == z) return false;
            x = z;
        }
        return true;
    }
    bool same(int x, int y){
        return find(x) == find(y);
    }
};

int main()
{
    int n,m,q;
    int a,b;
    cin >> n >> m;
    UnionFind uf(n);
    for(int i=0;i<m;i++){
        cin >> a >> b;
        uf.unite(a,b);
    }
    cin >> q;
    for(int i=0;i<q;i++){
        cin >> a >> b;
        if(uf.same(a,b)){
            cout << "yes\n";
        }else{
            cout << "no\n";
        }
    }
}

C++: #include<iostream>
#include<algorithm>
#include<queue>
using namespace std;
#define MAX 100000

struct Node{
	int group;
	queue<int> fr;
};

int N, M, Q, group_num = 0;
Node person[MAX];

void isFriend(int a, int b){
	if(person[a].group < 0 && person[b].group < 0){
		int p = a, next, m;
		queue<int> move;
		group_num++;
		person[p].group = group_num;
		//cout << a << " is group " << person[a].group << endl;
		move.push(p);

		while(!move.empty()){
			p = move.front();
			if(person[p].fr.empty()){
				move.pop();
			} else {
				m = person[p].fr.size();
				while(m--){
					next = person[p].fr.front();
					person[p].fr.pop();
					if(person[next].group < 0){
						person[next].group = group_num;
						//cout << next << " is group " << person[next].group << endl;
						move.push(next);
					}
				}
				move.pop();
			}
		}

		if(person[a].group == person[b].group){
			cout << "yes" << endl;
		} else {
			cout << "no" << endl;
		}
	} else if(person[a].group == person[b].group){
		cout << "yes" << endl;
	} else {
		cout << "no" << endl;
	}
}

int main(){
	cin >> N >> M;
	for(int i = 0; i < N; i++)
		person[i].group = -1;
	while(M--){
		int a, b;
		cin >> a >> b;
		person[a].fr.push(b);
		person[b].fr.push(a);
	}
	cin >> Q;
	while(Q--){
		int a, b;
		cin >> a >> b;
		isFriend(a, b);
	}
	return 0;
}