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>
using namespace std;
template <class A, class B> inline bool chmax(A &a, const B &b) { return b > a && (a = b, true); }
template <class A, class B> inline bool chmin(A &a, const B &b) { return b < a && (a = b, true); }
typedef long long ll;
typedef vector<int> vint;
typedef pair<int, int> pint;
typedef vector<long long> vlong;
#define _GLIBCXX_DEBUG
#define vpush(a,x) a.push_back(x);
#define rep(i, n) REP(i, 0, n)
#define all(v) v.begin(), v.end()
#define REP(i, x, n) for(int i = x; i < n; i++)
struct Unionfind{
    vector<int> rank,p,si;//木の高さの管理=rank,p=親の管理
    Unionfind(){}
        //初期化
    Unionfind(int size){
                rank.resize(size,0);
                p.resize(size,0);
              si.resize(size,1);
                for(int i=0;i<size;i++){
                        makeSet(i);
        }
    }
    void makeSet(int x){
                p[x]=x;//親を自分にする。
                rank[x]=0;//最初の高さは0
              si[x]=1;
    }
        //同じ集合か判定。
    bool same(int x,int y){
                return (findSet(x)==findSet(y));
    }
        //集合を併合
    void unite(int x,int y){
                link(findSet(x),findSet(y));
    }
    void link(int x,int y){
      if(x!=y){
              if(rank[x]<rank[y]){
                  p[x]=y;
                  si[y]+=si[x];
        }
              else{
                  p[y]=x;
                  if(rank[x]==rank[y]){
                     rank[y]++; 
            }
                  si[x]+=si[y];
        }
               
      }//cout<<rank[x]<<' '<<rank[y]<<'\n';
    }
          int siz(int x){
              int a=findSet(x); 
              return si[a];
    }             
        //経路圧縮
    int findSet(int x){
        //自分自身と親が等しくなるまで再帰
                if(x!=p[x]){
                        p[x]=findSet(p[x]);
                }
                return p[x];
    }
};
signed main(){
    cin.tie(0);
    ios::sync_with_stdio(false);
    int n,m;
    cin>>n>>m;
    Unionfind uf(n);
    int a,b;
    rep(i,m){
        cin>>a>>b;
        uf.unite(a,b);
    }
    int p;
    cin>>p;
    rep(i,p){
        cin>>a>>b;
        if(uf.same(a,b)){
            cout<<"yes"<<'\n';
        }
        else{
            cout<<"no"<<'\n';
        }
    }
    return(0);
}

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

const int NIL=-1;

int n, color[10000];
vector<int> G[100000];


void dfs(int v, int id){
    stack<int> s;
    s.push(v);
    color[v]=id;

    while(!s.empty()){
        int u=s.top(); s.pop();
        for(int i=0; i<G[u].size(); i++){
            int v1=G[u][i];
            if(color[v1]==NIL){
                color[v1]=id;
                s.push(v1);
            }    
        }
    }
}

void assignColor(){
    int id=1;

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

int main(void){
    int m; cin >> n >> m;

    for(int i=0; i<m; i++){
        int s,t; scanf("%d %d", &s, &t);
        G[s].push_back(t);
        G[t].push_back(s);
    }

    assignColor();

    int q; cin >> q;
    for(int i=0; i<q; i++){
        int s,t; scanf("%d %d", &s, &t);
        if(color[s]==color[t]) printf("yes\n");
        else printf("no\n");
    }
}

C++: #include<iostream>
#include<vector>
#include<stack>
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++){
    cin >> s >> t;
    if(color[s]==color[t]){
      cout << "yes" << endl;
    }else{
      cout << "no" << endl;
    }
  }
  return 0;
}