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<stdio.h>
#include<string.h>
#include<stdlib.h>
#include<math.h>
#include<stack>
#include<queue>
#include<vector>
#include<algorithm>
#include<string>
#include<iostream>
using namespace std;

int n,m,q;
static const int N=100005;
vector<int> G[N];
void branch(int a,int b){
    G[a].push_back(b);
    G[b].push_back(a);
}
int color[N];
void dfs(int r,int c){
    stack<int>s;
    s.push(r);
    while(!s.empty()){
        int u=s.top();s.pop();color[u]=c;
        for(int i=0;i<G[u].size();i++){
            if(color[G[u][i]]==0)s.push(G[u][i]);
        }
    }
}
void assigncolor(){
    int id=1;
    for(int u=0;u<n;u++){
        if(color[u]==0){
            dfs(u,id);
            id++;
        }
    }
}
void check(int a,int b){
    if(color[a]==color[b])printf("yes");
    else printf("no");
    printf("\n");
}
int main() {
    cin>>n>>m;
    for(int i=1;i<=m;i++){
        int a,b;cin>>a>>b;
        branch(a,b);
    }
    assigncolor();
    cin>>q;
    for(int i=1;i<=q;i++){
        int a,b;cin>>a>>b;check(a,b);
    }
    return 0;
}

C++: #include<iostream>
#define MAX 1000001
using namespace std;

int main() {
	int i, n, m, q, a, b, gnum = 0, ptog[MAX] = {};

	cin >> n >> m;
	for (i = 0; i < m; i++) {
		cin >> a >> b;
		if (ptog[a] != 0)ptog[b] = ptog[a];
		else if (ptog[b] != 0)ptog[a] = ptog[b];
		else ptog[a] = ptog[b] = ++gnum;
	}

	cin >> q;
	for (i = 0; i < q; i++) {
		cin >> a >> b;
		if (ptog[a] == ptog[b])cout << "yes\n";
		else cout << "no\n";
	}
}

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

static const int MAX =100000;
static const int NIL=-1;

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

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

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

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

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

  return 0;
}

C++: #include <iostream>
#include <cstdio>
#include <cstring>
#include <stack>
#include <vector>
using namespace std;
const int maxx = 100010;
int n, m;
int u, num, v;
int flag[maxx];
int color[maxx];
vector<int> G[maxx];

int c = 1;
void dfs(int i) {
	stack<int>s;
	s.push(i);
	color[i] = c;
	while (!s.empty()) {
		int u = s.top(); s.pop();
		int len = G[u].size();
		for (int i = 0; i < len; i++) {
			int v = G[u][i];
			if (flag[v] == 0) {
				color[v] = c;
				flag[v] = 1;
				s.push(v);
			}
		}
	}
}
int main()
{
	int q;
	memset(flag, 0, sizeof(flag));
	scanf("%d %d", &n, &m);
	for (int i = 0; i < m; i++) {
		scanf("%d %d", &u, &v);
		//?°???¶???v????????°G[u]??°??????
		G[u].push_back(v);
	}
	for (int i = 0; i < n; i++) {
		if (flag[i] == 0) {
			dfs(i);
			c++;
		}
	}
	scanf("%d", &q);
	for (int i = 0; i < q; i++) {
		scanf("%d %d", &u, &v);
		if (color[u] == color[v]) {
			printf("yes\n");
		}
		else {
			printf("no\n");
		}
	}
	return 0;
}

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

class UnionFind {
	vector<int> data;
	int root(int a) {
		return data[a] < 0 ? a : data[a] = root(data[a]);
	}
public:
	UnionFind(int n) : data(n, -1) {}
	bool Find(int a, int b) {
		return root(a) == root(b);
	}
	void Union(int a, int b) {
		int ra = root(a), rb = root(b);
		if (ra == rb) return;
		if (data[ra] < data[rb]) {
			data[ra] += data[rb];
			data[rb] = a;
		}
		else {
			data[rb] += data[ra];
			data[ra] = b;
		}
	}
};

int main()
{
	int n, m, q;
	cin >> n >> m;
	UnionFind uf(n);
	for (int i = 0, s, t; i < m;i++) {
		cin >> s >> t;
		uf.Union(s, t);
	}
	cin >> q;
	for (int i = 0, s, t; i < q; i++) {
		cin >> s >> t;
		if (uf.Find(s, t))
			cout << "yes" << endl;
		else
			cout << "no" << endl;
	}
	return 0;
}