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++: #define scanf_s scanf
#include <string>
#include <stdio.h>
#include <math.h>
#include <stack>
#include <queue>
#include <list>
#include <vector>
#include <iostream>
#include <algorithm>
using namespace std;

#define MAX 100000
#define _MAX 10000
struct Graph
{
	int id, k = 0;
	list<int> node;
	int d = -1;
};
Graph G[MAX];
list<int> co;
int bo = false;
void Connect(Graph *g,Graph *f)
{
	if (g->k >= 0) {
		int a = true;
		co.push_back(g -> id);
		for (auto i = g->node.begin(); i != g->node.end(); ++i) {
			if (&G[*i] == f) { bo = true; return; }
			for (auto j = co.begin(); j != co.end(); ++j) {
				if (*j == *i) {
					a = false;
					break;
				}
			}
			if(a) Connect(&G[*i], f);
			a = true;
		}
	}
}
int main(void)
{
	int n, m, q, a, b;
	int qq[_MAX] = { 0 };
	scanf_s("%d %d", &n, &m);
	for (int i = 0; i < m; ++i) {
		scanf_s("%d %d", &a, &b);
		G[a].id = a; G[b].id = b;
		++G[a].k; G[a].node.push_back(b);
		++G[b].k; G[b].node.push_back(a);
	}
	scanf_s("%d", &q);
	for (int i = 0; i < q; ++i) {
		scanf_s("%d %d", &a, &b);
		bo = 0;
		Connect(&G[a], &G[b]);
		qq[i] = bo;
		co.clear();
	}
	for (int i = 0; i < q; ++i) {
		if(qq[i]) printf("yes\n");
		else printf("no\n");
	}
}

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

using namespace std;

void dfs(int node, int group, const vector<vector<int>> & Es, vector<int> & groups){
    if (groups[node] != -1) return;
    groups[node] = group;
    for (auto new_node : Es[node]){
        dfs(new_node, group, Es, groups);
    }
}

void classify(int n, const vector<vector<int>> & Es, vector<int> & groups){
    for (int node = 0; node != n; ++node){
        dfs(node, node, Es, groups);
    }
}

int main()
{
    ios::sync_with_stdio(false);
    int n, m;
    cin >> n >> m;
    vector< vector<int> > Es(n);
    int s = 0, t = 0;
    for (int i = 0; i != m; ++i){
        cin >> s >> t;
        Es[s].push_back(t);
        Es[t].push_back(s);
    }
    vector<int> groups(n, -1);
    classify(n, Es, groups);
    int q = 0;
    cin >> q;
    for (int i = 0; i != q; ++i){
        cin >> s >> t;
        if (groups[s] == groups[t]){
            cout << "yes" << endl;
        }else{
            cout << "no" << endl;
        }
    }
    
    return 0;
}

C++: #include <iostream>
#include <vector>
using namespace std;

class UnionFind {
 public:
    int g_num;
    vector<int> rank, par;

    UnionFind() {}
    UnionFind(int size) {
        rank.resize(size, 0);
        par.resize(size, 0);
        for (int i = 0; i < size; i++) {
            par[i] = i;
            rank[i] = 0;
        }
        g_num = size;
    }

    bool same(int x, int y) {
        return find(x) == find(y);
    }

    void unite(int x, int y) {
        x = find(x);
        y = find(y);
        if (x == y) return;

        g_num--;
        if (rank[x] > rank[y]) {
            par[y] = x;
        } else {
            par[x] = y;
            if (rank[x] == rank[y]) rank[y]++;
        }
    }

    int find(int x) {
        if (x == par[x]) return x;
        return par[x] = find(par[x]);
    }

    int group_num() {
        return g_num;
    }
};

int main(void) {
    int n, m, a, b, q;
    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;
        cout << (uf.same(a, b) ? "yes":"no") << endl;
    }
    return 0;
}

C++: #include<bits/stdc++.h>
using namespace std;
int main()
{
	int n,m;
	cin>>n>>m;
	int parent[n];
	for(int i=0;i<n;i++)
	{
		parent[i] = -1;
	}
	int first,second;
	for(int i=0;i<m;i++)
	{
		cin>>first>>second;
		while(parent[first]!=-1)
		{
			first=parent[first];
		}
		while(parent[second]!=-1)
		{
			second=parent[second];
		}
		if(second!=first)
		{
			parent[second]=first;
		}
	}
	int cases,first1,second1;
	cin>>cases;
	for(int i=0;i<cases;i++)
	{
		cin>>first1>>second1;
		while(parent[first1]!=-1)
		{
			first1=parent[first1];
		}
		while(parent[second1]!=-1)
		{
			second1=parent[second1];
		}
		if(first1==second1)
			cout<<"yes";
		else
			cout<<"no";
		cout<<endl;
	}
}