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<iomanip>
#include<algorithm>
#include<bitset>
#include<cctype>
#include<cmath>
#include<cstdio>
#include<cstring>
#include<functional>
#include<limits>
#include<list>
#include<map>
#include<set>
#include<stack>
#include<string>
#include<sstream>
#include<queue>
#include<vector>
using namespace std;

#define MOD 1000000007
#define INF 0x3f3f3f3f
#define INFL 0x3f3f3f3f3f3f3f3fLL

#define MAX 100000
#define NIL -1

/*

G':1-2-4 3-5
color:1 2

*/

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

void dfs(int u, int c) {
	stack<int> S;
	S.push(u);
	color[u] = 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);
			}
		}
	}
}

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

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

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

	return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for(int i=0; i<(n); i++)

#define MAX 100000
#define NIL -1

void dfs(int start_point, int id, vector<int> *graph, int *color, int n){
    
    stack<int> S;
    S.push(start_point);
    color[start_point] = id;

    while(!S.empty()){
        int node = S.top(); S.pop();
        rep(i, graph[node].size()){
            int v = graph[node][i];
            if(color[v] == NIL){
                color[v] = id;
                S.push(v);
            }
        }
    }
}

void assignColor(vector<int> *graph, int *color, int n){
    int id = 1;
    rep(i, n){
        if(color[i] == NIL){
            dfs(i, id++, graph, color, n);
        }
    }
}

int main() {

    int n, m;
    cin >> n >> m;
    vector<int> graph[MAX];
    int color[MAX];
    rep(i, n){
        color[i] = NIL;
    }

    rep(i, m){
        int s, t;
        cin >> s >> t;
        graph[s].push_back(t);
        graph[t].push_back(s);
    }

    assignColor(graph, color, n);

    int q;
    cin >> q;
    rep(i, q){
        int x, y;
        cin >> x >> y;
        if(color[x] == color[y]){
            cout << "yes" << endl;
        }
        else{
            cout << "no" << endl;
        }
    }

    return 0;
}

C++: #include <bits/stdc++.h>

#define REP(i, n) for(int i=0;i<(int)(n);i++)
#define ALL(x) (x).begin(),(x).end()
const int INF = 1e9;

using namespace std;
int n, m;
struct node {
    int parent;
    vector<int> child;
};

int main() {
    cin >> n >> m;
    node person[n];
    REP(i, n)
        person[i].parent = -1;
    REP(i, m){
        int s, t;
        cin >> s >> t;
        if(person[s].parent == -1 && person[t].parent == -1){
            person[s].parent = s;
            person[t].parent = s;
            person[s].child.push_back(t);
        } else if(person[s].parent == -1){
            person[s].parent = person[t].parent;
            person[t].child.push_back(s);
        } else if(person[t].parent == -1){
            person[t].parent = person[s].parent;
            person[s].child.push_back(t);
        } else {
            person[t].parent = person[s].parent;
            REP(j, person[t].child.size()){
                person[person[t].child[j]].parent = person[s].parent;
                person[s].child.push_back(person[t].child[j]);
            }
        }
    }
    int q;
    cin >> q;
    REP(i, q){
        int s, t;
        cin >> s >> t;
        if(person[s].parent != -1 && person[t].parent != -1  && person[s].parent == person[t].parent)
            cout << "yes" << endl;
        else
            cout << "no" << endl;
    }
    return 0;
}

C++: #include <iostream>
#include <vector>
#include <algorithm>
#include <queue>
#include <stack>
#include <stdio.h>
#include <cmath>
#include <set>
#include <map>
using namespace std;

vector<vector<int> >g;
int n,m,q;

vector<bool>visited;
bool dfs(int s,int t){
    if(s==t)return true;
    visited[s]=true;
    for(int i=0;i<g[s].size();i++){
        if(!visited[g[s][i]]){
            if(dfs(g[s][i],t)){
                return true;
            }
        }
    }
    return false;
}
int main() {
    cin>>n>>m;
    g.resize(n);
    
    for(int i=0;i<m;i++){
        int s,t;
        cin>>s>>t;
        g[s].push_back(t);
        g[t].push_back(s);
    }
    cin>>q;
    for(int i=0;i<q;i++){
        visited.resize(n,false);
        int s,t;
        cin>>s>>t;
        string ret =(dfs(s,t)?"yes":"no");
        if(ret=="no")return 1;
        else cout<<ret<<endl;
    }
    return 0;
}