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<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;
}

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

struct Graph {
    vector<vector<int>> adj;
    vector<int> color;
    int colorID;
    Graph(int n) {
        adj.assign(n, vector<int>());
        color.assign(n, -1);
        colorID = 0;
    }
};

void dfs(Graph& g, int u, int colorID)
{
    g.color[u] = colorID;
    for (auto v : g.adj[u]) {
        if (g.color[v] == -1) {
            g.color[v] = colorID;
            dfs(g, v, colorID);
        }
    }
}

int main()
{
    int n, k;
    cin >> n >> k;
    Graph g(n);
    for (int i = 0; i < k; i++) {
        int u, v;
        cin >> u >> v;
        g.adj[u].push_back(v);
        g.adj[v].push_back(u);
    }

    for (int u = 0; u < n; u++) {
        if (g.color[u] == -1) {
            dfs(g, u, g.colorID++);
        }
    }

    int q;
    cin >> q;
    for (int i = 0; i < q; i++) {
        int u, v;
        cin >> u >> v;
        if (g.color[u] == g.color[v]) {
            cout << "yes" << endl;
        } else {
            cout << "no" << endl;
        }
    }
}

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

using ll = long long;
using namespace std;

/* initialize */
vector<int> A[100000];
int c[100000];
/* main */
void dfs(int r, int d){
    stack<int> S;
    S.push(r);
    c[r] = d;
    while (!S.empty()){
        int u = S.top(); S.pop();
        for (int v : A[u]) {
            if ( c[v] == -1){
                c[v] = d;
                S.push(v);
            }
        }
    }
}
int main() {
    int n, m, k, l;
    cin >> n;
    cin >> m;
    for (int i = 0; i < m; ++i) {
        scanf("%d %d", &k, &l);
        A[k].push_back(l);
        A[l].push_back(k);
    }
    int id = 1;
    for (int i = 0; i < n; ++i) {
        c[i] = -1;
    }
    for (int j = 0; j < n; ++j) {
        if (c[j] == -1) dfs(j,id++);
    }
    int q;
    cin >> q;
    for (int i = 0; i < q; ++i) {
        cin >> k >> l;
        if(c[k] == c[l]) cout << "yes\n";
        else cout << "no\n";
    }
    return 0;
}

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

vector<int> G[100000], color(100000);
int c;
void dfs(int v) {
    color[v] = c;
    for (int i = 0; i < G[v].size(); ++i) {
        int e = G[v][i];
        if (!color[e]) dfs(e);
    }
}
int main() {
    int n, m;
    cin >> n >> m;
    while (m--) {
        int s, t;
        cin >> s >> t;
        G[s].push_back(t);
        G[t].push_back(s);
    }
    for (int i = 0; i < n; ++i) {
        if (!color[i]) {
            c++;
            dfs(i);
        }
    }
    int q;
    cin >> q;
    while (q--) {
        int s, t;
        cin >> s >> t;
        if (color[s] == color[t]) cout << "yes" << endl;
        else cout << "no" << endl;
    }
    return 0;
}

C++: #include <cstdio>
#include <queue>
#include <vector>

typedef struct{
	std::vector<int> neighbors;
	int cluster;
} node;

void dfs(node* nodes, int id, int cluster){
	for (int i=0; i<nodes[id].neighbors.size(); i++){
		if (nodes[nodes[id].neighbors[i]].cluster == -1){
			nodes[nodes[id].neighbors[i]].cluster = cluster;
			dfs(nodes, nodes[id].neighbors[i], cluster);
		}
	}
}

int main(){
	int n, d, num_relation, n_query, s, t, cluster;
	node *nodes;

	scanf("%d %d", &n, &num_relation);
	nodes = new node[n];
	for (int i=0; i<n;i++){
		nodes[i].cluster = -1;
	}
	for(int i=0;i<num_relation;i++){
		scanf("%d %d", &s, &t);
		nodes[s].neighbors.push_back(t);
		nodes[t].neighbors.push_back(s);
	}
	cluster = -1;
	for (int i=0;i<n;i++){
		cluster ++;
		if (nodes[i].cluster == -1) dfs(nodes, i, cluster);
	}
	scanf("%d", &n_query);
	for(int i=0;i<n_query;i++){
		scanf("%d %d", &s, &t);
		if (nodes[s].cluster != -1 && nodes[s].cluster != -1 && nodes[s].cluster == nodes[t].cluster) printf("yes\n");
		else printf("no\n");

	}

	delete []nodes;
	return 0;
}