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<iostream>
#include<string>
#include<cstdio>
#include<algorithm>
#include<queue>
using namespace std;


int n;

string *color;

queue<int> q;

int *ans;

vector<int> g[1000000];


void bfs(int x){
  color[x] = "gray";
  q.push(x);


  while(q.size() != 0){
    int u = q.front();
    q.pop();

    for(int i = 0; i < g[u].size(); i++){
      int v = g[u][i];
      if(color[v] == "white"){
        color[v] = "gray";
        q.push(v);
      }
    }

    color[u] = "black";
    ans[u] = x;


  }
  return;
}


int main(){

  cin >> n;

  color = new string[n];

  ans = new int[n];

  int m;

  cin >> m;


  int a, b;


  for(int i = 0; i < m; i++){
    cin >> a >> b;
    g[a].push_back(b);
    g[b].push_back(a);
  }


  for(int i = 0; i < n; i++){
    color[i] = "white";
  }


  for(int j = 0; j < n; j++){
    if(color[j] == "white"){
      bfs(j);
    }
  }

  int q;

  cin >> q;

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

  return 0;
}

C++: #include <cassert>
#include <cstdio>
#include <algorithm>
#include <iostream>
#include <vector>
#include <list>

class TVertex
{
    int FIndex;
    int FCommuniyId;
    std::list<TVertex*> FList;

public:
    TVertex(int Index)
     : FIndex(Index), FCommuniyId(0)
    {}
    void AddPath(TVertex* Vertex)
    {
        FList.push_back(Vertex);
    }
    void SetCommunity(int CommunityId)
    {
        if(FCommuniyId) return;
        FCommuniyId = CommunityId;
        for(std::list<TVertex*>::iterator It = FList.begin(); It != FList.end(); ++It){
            TVertex* V = *It;
            V->SetCommunity(CommunityId);
        }
    }
    int CommunityId()const
    {
        return FCommuniyId;
    }
};
class TGraph
{
    std::vector<TVertex*> FTable;
    void Init(int n)
    {
        assert(n > 0);
        FTable.resize(n);
        for(int i = 0; i < n; ++i){
            FTable[i] = new TVertex(i);
        }
    }
public:
    TGraph(int n)
    {
        Init(n);
    }
    void MakeFriend(int s, int t)
    {
        assert(s < FTable.size());
        assert(t < FTable.size());
        FTable[s]->AddPath(FTable[t]);
        FTable[t]->AddPath(FTable[s]);
    }
    void SetCommunity()
    {
        for(std::size_t i = 0; i < FTable.size(); ++i){
            FTable[i]->SetCommunity(i+1);
        }
    }
    bool IsSameCommunity(int s, int t)const
    {
        assert(s < FTable.size());
        assert(t < FTable.size());
        return FTable[s]->CommunityId() == FTable[t]->CommunityId();
    }
};

int main()
{
    int n, m;
    std::scanf("%d %d", &n, &m);
    TGraph Graph(n);
    for(int i = 0; i < m; ++i){
        int s, t;
        std::scanf("%d %d", &s, &t);
        Graph.MakeFriend(s, t);
    }
    int q;
    std::scanf("%d", &q);
    Graph.SetCommunity();
    for(int i = 0; i < q; ++i){
        int s, t;
        std::scanf("%d %d", &s, &t);
        std::printf("%s\n", (Graph.IsSameCommunity(s, t) ? "yes" : "no"));
    }
    return 0;
    
}

C++: #include <iostream>
#include <algorithm>
#include <vector>
#include<string>
#include <set>
#include <map>
#include <queue>
#include <limits.h>
#include <cmath>

using namespace std;

#define rip(i,n,s) for (int i=(s);i<(int)(n);i++)
#define all(a) (a).begin(),(a).end()
typedef long long ll;

struct UnionFind{
    int size;
    vector<int> par;
    vector<int> rank;
    UnionFind(int x){
        size=x;
        par=vector<int> (x);
        rank=vector<int> (x,1);
        for (int i=0;i<x;i++){
            par[i]=i;
        }
    }
    int root(int x){
        if(par[x]==x){
            return x;
        }
        else{
            return par[x]=root(par[x]);
        }
    }
    void unite(int x,int y){
        x=root(x);y=root(y);
        if(x==y){
            return;
        }
        if(rank[x]<rank[y]){
            par[x]=y;
        }
        else{
            par[y]=x;
        }
        if(rank[x]==rank[y]){
            rank[x]++;
        }
    }
    bool check(int x,int y){
        return root(x)==root(y);
    }
    void initialize(){
        for (int i=0;i<size;i++){
            par[i]=i;
        }
    }
};

int main(){
    int n,m;
    cin >> n >> m;
    UnionFind uf(n);
    int a,b;
    rip(i,m,0){
        cin >> a >> b;
        uf.unite(a,b);
    }
    int q;
    cin >> q;
    vector<bool> ans(q);
    rip(i,q,0){
        cin >> a >> b;
        ans[i]=uf.check(a,b);
    }
    rip(i,q,0){
        if(ans[i]){
            printf("yes\n");
        }
        else{
            printf("no\n");
        }
    }
}