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<iostream>
#include<cstdio>
#include<vector>
#include<queue>
#define Lens 100005

using namespace std;
int n, m, q;
vector<int> A[Lens];
queue<int>	Q;
char c[Lens], d[Lens];

int Find(int s, int t)
{
	Q.push(s);
	c[s] = 'g';
	while (!Q.empty())
	{
		s = Q.front();
		Q.pop();
		c[s] = 'g';
		for (int j = 0; j < A[s].size(); j++)
		{
			if (c[A[s][j]] == 'w')
				Q.push(A[s][j]);
			if (A[s][j] == t)
			{
				return 1;
			}
		}
	}
return 0;
}

int main()
{
	cin >> n >> m;
	for (int i = 0; i < m; i++)
	{
		int s, t;
		cin >> s >> t;
		d[s] = d[t] = 'w';
		A[s].push_back(t);
		A[t].push_back(s);
	}
	cin >> q;
	for (int i = 0; i < q; i++)
	{
		for (int j = 0; j < n; j++)
			c[j] = d[j];
		int s, t;
		cin >> s >> t;
		if (Find(s, t))
			cout << "yes" << endl;

		else
			cout << "no" << endl;
	}
	return 0;
}

C++: #include<vector>

class UnionFind {
public:
    UnionFind(int N) :parent(N), rank(N, 0), size(N, 1) {
        for (int i = 0; i < N; ++i) parent[i] = i;
    }
    int find(int x) {
        return x == parent[x] ? x : parent[x] = find(parent[x]);
    }
    bool same(int x, int y) {
        return find(x) == find(y);
    }
    void unite(int x, int y) {
        x = find(x), y = find(y);
        if (x == y) return;
        if (rank[x] < rank[y]) parent[x] = y;
        else {
            parent[y] = x;
            if (rank[x] == rank[y]) rank[x]++;
            std::swap(x, y);
        }
        size[y] += size[x];
        size[x] = 0;
    }
    int getParentRank(int x) {
        return rank[find(x)];
    }
    int getParentSize(int x) {
        return size[find(x)];
    }
    int getSize(int x) {
        return size[x];
    }
private:
    std::vector<int> parent, rank, size;
};
#include<iostream>
using namespace std;
int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    int n,m;
    cin>>n>>m;
    UnionFind UF(n);
    for(int i=0;i<m;++i){
        int a,b;
        cin>>a>>b;
        UF.unite(a,b);
    }
    int q;
    cin>>q;
    for(int i=0;i<q;++i){
        int a,b;
        cin>>a>>b;
        cout<<(UF.same(a,b)?"yes":"no")<<endl;
    }
}

C++: #include<bits/stdc++.h>
using namespace std;
typedef long long ll;
#define loop(i,a,b) for(i=a;i<b;i++)
#define rloop(i,a,b) for(i=a;i>=b;i--)
#define vi vector<int>
#define vl vector<ll>
#define vii vector< vector<int> >
#define vll vector< vector<ll> >
#define vs vector<string>
const int inf=1000000001;
const ll INF=1e16;
#define MOD 1000000007
#define mod 1000000009
#define pi 3.14159265358979323846
static const int WHITE=0;
static const int GRAY=1;
static const int BLACK=2;
static const int N=100000;

int n;
vii v(N,vi());
vi color(N),nt(N);

bool dfs(int,int);
int next(int);

int main(){
	int m,i,j;
	cin>>n>>m;
	int s,t;
	loop(i,0,m){
		cin>>s>>t;
		v[s].push_back(t);
		v[t].push_back(s);
	}
	int q;
	cin>>q;
	loop(i,0,q){
		cin>>s>>t;
		bool flag=dfs(s,t);
		if(flag==true){
			cout<<"yes"<<endl;
		}else{
			cout<<"no"<<endl;
		}
	}
}

bool dfs(int s,int t){
	if(s==t){
		return true;
	}
	int i;
	loop(i,0,n+1){
		color[i]=WHITE;
	}
	stack<int> st;
	st.push(s);
	color[s]=GRAY;
	while(!st.empty()){
		int u=st.top();
		int u2=next(u);
		if(u2==t){
			return true;
		}else if(u2!=-1){
			color[u2]=GRAY;
			st.push(u2);
		}else{
			color[u]=BLACK;
			st.pop();
		}
	}
	return false;
}

int next(int u){
	int i;
	loop(i,0,v[u].size()){
		if(color[v[u][i]]==WHITE){
			return v[u][i];
		}
	}
	return -1;
}