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 <cstring>
#include <iostream>
#include <vector>

int main() {
    int n, m;
    std::cin >> n >> m;

    int link[n];
    std::vector<std::vector<int>> list;
    for (int i = 0; i < n; i++) {
        link[i] = -1;
    }

    int cnt = 0;
    int s, t;
    for (int i = 0; i < m; i++) {
        std::cin >> s >> t;
        if (link[s] == -1 && link[t] == -1) {
            link[s] = link[t] = cnt;
            cnt++;
            list.emplace_back(std::vector<int>({s, t}));
        } else if (link[s] == -1) {
            link[s] = link[t];
            list[link[t]].emplace_back(s);
        } else if (link[t] == -1) {
            link[t] = link[s];
            list[link[s]].emplace_back(t);
        } else if (link[s] < link[t]) {
            list[link[s]].insert(list[link[s]].end(), list[link[t]].begin(), list[link[t]].end());
            for (auto val : list[link[t]]) {
                link[val] = link[s];
            }
        } else if (link[t] < link[s]) {
            list[link[t]].insert(list[link[t]].end(), list[link[s]].begin(), list[link[s]].end());
            for (auto val : list[link[s]]) {
                link[val] = link[t];
            }
        }
    }

    int q;
    std::cin >> q;
    for (int i = 0; i < q; i++) {
        std::cin >> s >> t;
        if (link[s] == link[t] && link[s] != -1) {
            std::cout << "yes" << std::endl;
        } else {
            std::cout << "no" << std::endl;
        }
    }
}

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

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

int main(void){
    int n,m,q,s,t,i,rs,rt;
    cin>>n>>m;
    int par[100000];
    for(i=0;i<n;i++)par[i]=i;
    
    for(i=0;i<m;i++){
        cin>>s>>t;
        rs=root(s,par),rt=root(t,par);
        if(rs!=rt)par[rs]=rt;
    }

    for(i=0;i<n;i++){
        par[i]=root(i,par);
    }
    
    cin>>q;
    for(i=0;i<q;i++){
        cin>>s>>t;
        if(par[s]==par[t]){
            cout<<"yes"<<endl;
        }
        else{
            cout<<"no"<<endl;
        }
    }
    
    return 0;
}

C++: #include <iostream>
#include <stack>
#include <vector>
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);
			}
		}
	}
	return;
}

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++);
	}
	return;
}

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

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

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

int main() {
	int s, t, m, q, i;

	cin >> n >> m;

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

	assignColor();

	cin >> q;

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

	return 0;
}

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

std::vector<int> v[100010];
int n;
int m;

bool visited[10010];

/**
bool dfs(int from, int to) {

  if(visited[to]) {
    return true;
  }

  visited[from] = true;
  for(int u=0; u<v[from].size(); ++u) {
    if(visited[v[from][u]]) continue;
    else {
      visited[v[from][u]] = true;
      dfs(v[from][u], to);
    }
  }

  return false;
}
**/

void dfs(int from) {
  visited[from] = true;
  for(int u=0; u<v[from].size(); ++u) {
    if(visited[v[from][u]]) continue;
    else {
      dfs(v[from][u]);
    }
  }
}

int main() {
  std::cin >> n >> m;

  for(int i=0; i<m; ++i) {
    int from, to;
    std::cin >> from >> to;
    v[from].push_back(to);
    v[to].push_back(from);
  }

  int q_n;
  std::cin >> q_n;
  bool answers[10010];
  for(int i=0; i<q_n; ++i) {
    int from, to;
    std::cin >> from >> to;
    for(int j=0; j<n; ++j) visited[j] = false;

    dfs(from);
    answers[i] = visited[to];
  }

  for(int i=0; i<q_n; ++i) {
    if(answers[i]) std::cout << "yes" << std::endl;
    else std::cout << "no" << std::endl;
  }

}