Go: package main

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
)

var (
	n     int
	G     [100000][]int
	color [100000]*int
)

func dfs(r int, c int) {
	S := Stack{}
	S.Push(r)
	color[r] = &c
	for !S.IsEmpty() {
		u := S.Pop()
		for i := 0; i < len(G[u]); i++ {
			v := G[u][i]
			if color[v] == nil {
				color[v] = &c
				S.Push(v)
			}
		}
	}
}

func assignColor() {
	id := 1
	for i := 0; i < n; i++ {
		color[i] = nil
	}
	for u := 0; u < n; u++ {
		if color[u] == nil {
			id++
			dfs(u, id)
		}
	}
}

func main() {
	sc := bufio.NewScanner(os.Stdin)
	sc.Split(bufio.ScanWords)
	sc.Scan()
	n, _ = strconv.Atoi(sc.Text())
	sc.Scan()
	r, _ := strconv.Atoi(sc.Text())

	for i := 0; i < r; i++ {
		sc.Scan()
		s, _ := strconv.Atoi(sc.Text())
		sc.Scan()
		t, _ := strconv.Atoi(sc.Text())
		G[s] = append(G[s], t)
		G[t] = append(G[t], s)
	}
	assignColor()
	sc.Scan()
	qNum, _ := strconv.Atoi(sc.Text())
	for i := 0; i < qNum; i++ {
		sc.Scan()
		s, _ := strconv.Atoi(sc.Text())
		sc.Scan()
		t, _ := strconv.Atoi(sc.Text())
		if color[s] == color[t] {
			fmt.Println("yes")
		} else {
			fmt.Println("no")
		}
	}
}

// Stack is Stack
type Stack struct {
	stack []int
}

// Push new value
func (stack *Stack) Push(val int) {
	stack.stack = append(stack.stack, val)
}

// Pop new value
func (stack *Stack) Pop() int {
	val := stack.stack[len(stack.stack)-1]
	stack.stack = stack.stack[0 : len(stack.stack)-1]
	return val
}

// IsEmpty return true when stack is empty
func (stack *Stack) IsEmpty() bool {
	return len(stack.stack) == 0
}

C++: //#define scanf_s scanf
#include <string>
#include <stdio.h>
#include <math.h>
#include <stack>
#include <queue>
#include <list>
#include <vector>
#include <iostream>
#include <algorithm>
using namespace std;

#define MAX 100
#define _MAX 1000
struct Graph
{
	int id, k = 0;
	list<int> node;
	int d = -1;
};
Graph G[MAX];
list<int> co;
int bo = false;
void Connect(Graph *g,Graph *f)
{
	if (g->k >= 0) {
		int a = true;
		co.push_back(g -> id);
		printf("%d,", g->id);
		for (auto i = g->node.begin(); i != g->node.end(); ++i) {
			if (&G[*i] == f) { bo = true; return; }
			for (auto j = co.begin(); j != co.end(); ++j) {
				if (*j == *i) {
					a = false;
					break;
				}
			}
			if(a) return Connect(&G[*i], f);
			a = true;
		}
	}
}
int main(void)
{
	int n, m, q, a, b;
	int qq[_MAX] = { 0 };
	scanf_s("%d %d", &n, &m);
	for (int i = 0; i < m; ++i) {
		scanf_s("%d %d", &a, &b);
		G[a].id = a; G[b].id = b;
		++G[a].k; G[a].node.push_back(b);
		++G[b].k; G[b].node.push_back(a);
	}
	scanf_s("%d", &q);
	for (int i = 0; i < q; ++i) {
		scanf_s("%d %d", &a, &b);
		bo = 0;
		Connect(&G[a], &G[b]);
		qq[i] = bo;
		co.clear();
	}
	for (int i = 0; i < q; ++i) {
		if(qq[i]) printf("yes\n");
		else printf("no\n");
	}
}

C++: #include<iostream>
#include<map>
#include<set>

using namespace std;

int main(){
	int n, m, s, t, q, i, j;
	int id, stc = 0;
	bool answer_yes = false;
	map<int, set<int> > Adj;
	map<int, int> Stack;
	set<int> Check;
	set<int>::iterator it, itend;

	cin >> n >> m;
	for (i = 0; i < m; i++) {
		cin >> s >> t;
		Adj[s].insert(t);
		Adj[t].insert(s);
	}

	/*for (auto it1 = Adj.begin(); it1 != Adj.end(); it1++) {
		cout << "\n" << it1->first << " : " << flush;
		for (auto it2 = it1->second.begin(); it2 != it1->second.end(); it2++) {
			cout << *it2 << " " << flush;
		}
	}
	cout << endl;*/

	cin >> q;
	for (i = 0; i < q; i++) {
		cin >> s >> t;
		
		// calculate
		Stack.insert(pair<int, int>(stc, s));
		Check.insert(s);
		while (!Stack.empty()) {
			id = Stack[stc];
			//cout << "\nid : " << id << " stc : " << stc << endl;
			itend = Adj[id].end();
			for (it = Adj[id].begin(); it != itend; it++) {
				//cout << *it << " " << flush;
				if (Check.find(*it) == Check.end()) {
					if (*it == t) {
						answer_yes = true;
						Stack.clear();
						break;
					}
					stc++;
					Stack.insert(pair<int, int>(stc, *it));
					Check.insert(*it);
					break;
				}
			}
			if (it == itend) {
				Stack.erase(stc);
				stc--;
			}
		}
		if (answer_yes) {
			cout << "yes" << endl;
		} else {
			cout << "no" << endl;
			Stack.clear();
		}
		answer_yes = false;
		Check.clear();
		stc = 0;
	}
	
	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;
};

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[s].parent = s;
            person[t].parent = s;
        }
        else
            person[t].parent = person[s].parent;
    }
    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 <bits/stdc++.h>
using namespace std;

const int MAX=100005;
vector<int> S[MAX];

int par[MAX];
int root(int a){
    if(par[a]==a) return a;
    else return par[a]=root(par[a]);
}
void unite(int a,int b){
    if(root(a)!=root(b)) par[root(b)]=root(a);
}
bool check(int a,int b){
    return root(a)==root(b);
}

int main(){

    int N,M;cin>>N>>M;
    for(int i=0;i<N;i++){
        par[i]=i;
    }
    for(int i=0;i<M;i++){
        int a,b;cin>>a>>b;
        unite(a,b);
    }
    int Q;cin>>Q;
    for(int i=0;i<Q;i++){
        int a,b;cin>>a>>b;
        if(check(a,b)) cout<<"yes"<<endl;
        else cout<<"no"<<endl;
    }

}

C++: #include <bits/stdc++.h>
#define ll long long
#define INF 999999999
#define MOD 1000000007

using namespace std;

typedef pair<int,int>P;

const int MAX_N = 100000;

int par[MAX_N];
int rank[MAX_N];

void initial(int n){		//?????????
	for(int i=0;i<n;i++){
		par[i] = i;
		rank[i] = 0;
	}
}

int find(int x){		//??¨??????????±???????
	if(par[x] == x){
		return x;
	}else{
		return par[x] = find(par[x]);
	}
}

void unite(int x,int y){
	x = find(x);
	y = find(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 same(int x,int y){
	return find(x) == find(y);
}

int main()
{
	int n,m,q;
	int a,b;
	cin >> n;
	cin >> m;
	initial(n);
	for(int i=0;i<m;i++){
		cin >> a;
		cin >> b;
		unite(a,b);
	}
	cin >> q;
	for(int i=0;i<q;i++){
		cin >> a;
		cin >> b;
		if(same(a,b)){
			cout << "yes\n";
		}else{
			cout << "no\n";
		}
	}
}

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

std::queue<int> q;
typedef struct{
	bool isVisited;
	std::vector<int> neighbors;
} node;

void bfs(node* nodes, int t){
	int id;
	while (!q.empty()){
		id = q.front();
		q.pop();
		if (!nodes[t].isVisited){
			for (int i=0; i<nodes[id].neighbors.size(); i++){
				if (!nodes[nodes[id].neighbors[i]].isVisited){
					q.push(nodes[id].neighbors[i]);
					nodes[nodes[id].neighbors[i]].isVisited=true;
				}
			}
		}
	}
	if (nodes[t].isVisited) printf("yes\n");
	else printf("no\n");
}

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

	scanf("%d %d", &n, &num_relation);
	nodes = new node[n];
	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);
	}

	scanf("%d", &n_query);
	for(int i=0;i<n_query;i++){
		for (int j=0; j<n;j++){
			nodes[j].isVisited=false;
		}
		scanf("%d %d", &s, &t);
		q.push(s);
		bfs(nodes, t);
	}

	delete []nodes;
	return 0;
}