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>
#include<cstdio>
using namespace std;
static const int MAX = 1000000;
static const int NIL = -1;

int n;
vector<int> G[MAX];     //頂点数を1000000とする
                        //隣接リスト
int color[MAX];

void dfs( int r, int c ) {
    stack<int> S;
    S.push(r);          //始点rをスタックに追加
    color[r] = c;       //色をいれる
    while ( !S.empty() ) {
        int u = S.top();
        S.pop();        //スタックから頂点uを取り出し訪問
        for ( int i = 0; i < G[u].size(); ++i ) {
            int v = G[u][i];
            //頂点uに隣接する頂点vを探索
            if ( color[v] == NIL ) {
                color[v] = c;
                S.push(v);//id(色)は変わらない
            }
        }
    }
}

void assignColor() {
    int id = 1;             //全てにNIL
    for ( int i = 0; i < n; ++i ) color[i] = NIL;
    for ( int u = 0; u < n; ++u ) {
        if ( color[u] == NIL ) dfs( u , id++ ); //id(色)にかぶりがないように
    }
}

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

    scanf("%d %d",&n,&m);

    for ( int i = 0; i < m; ++i ) {
        scanf("%d %d",&s,&t);
        G[s].push_back(t);  // s → tへ辺
        G[t].push_back(s);  // t → sへ辺
    }

    assignColor();

    scanf("%d",&q);

    for ( int i = 0; i < q; ++i ) {
        scanf("%d %d",&s,&t);
        if ( color[s] == color[t] ) {
            puts("yes");
        } else {
            puts("no");
        }
    }

    return 0;
}

C++: #include<iostream>
#include<cstdio>
#include<vector>
#include<queue>
#define Lens 1005
#define Nil -1

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

void bns(int k, int v)
{
	Q.push(k);
	c[k] = v;
	while (!Q.empty())
	{
		k = Q.front();
		Q.pop();
		c[k] = v;
		for (int i = 0; i < A[k].size(); i++)
		{
			int tmp = A[k][i];
			if (c[tmp] == Nil)
			{
				Q.push(tmp);
			}
		}
	}
}

int main()
{
	int v = 1;
	cin >> n >> m;
	for (int i = 0; i < m; i++)
	{
		int s, t;
		cin >> s >> t;
		c[s] = c[t] = Nil;
		A[s].push_back(t);
		A[t].push_back(s);
	}
	for (int i = 0; i < n; i++)
	{
		if (c[i] == Nil)
		{
			bns(i, v);
			v++;
		}

	}
	cin >> q;
	for (int i = 0; i < q; i++)
	{
		int s, t;
		cin >> s >> t;

		if (c[s] == c[t]&&c[s]!=Nil&&c[s]!=0)
			cout << "yes" << endl;
		else
			cout << "no" << endl;
	}
	return 0;
}

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

using namespace std;
struct user {
    user() {};
    user(int i) : id {i}, fs {}, group {-1} {};
    int id;
    vector<int> fs;
    int group;
};

void add_friends(user *us, int x, int y){
    us[x].fs.push_back(y);
    us[y].fs.push_back(x);
}

void dfs(user* us, int id, int g){
    if(us[id].group == g){
        return;
    }
    us[id].group = g;
    vector<int> fs = us[id].fs;
    for(auto x : fs){
        dfs(us, x, g);
    }
}

void make_group(user* us, int n){
    int g = 0;
    for(int i = 0; i < n; ++i){
        if(us[i].group < 0){
            dfs(us, i, g);
            ++g;
        }
    }
}

int main(){
    int n, m;
    cin >> n >> m;
    user us[n];
    for(int i = 0; i < n; ++i){
        us[i] = user(i);
    }
    for(int i = 0; i < m; ++i){
        int a, b;
        cin >> a >> b;
        add_friends(us, a, b);
    }
    make_group(us, n);
    int q;
    cin >> q;
    for(int i = 0; i < q; ++ i){
        int a, b;
        cin >> a >> b;
        if(us[a].group == us[b].group){
            cout << "yes" << endl;
        } else {
            cout << "no" << endl;
        }
    }
}

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

int main(){
	int n,m,q,i,j;
	int s,t;
	vector<int> L(100005,-1);
	cin >> n >> m;
	
	for (j=0;j<n;j++){
		L[j]=j;
	}
	
	for (i=0;i<m;i++){
		cin >> s >> t ;
		if (L[s]!=L[t]){
			int a=L[t];
			for (j=0;j<n;j++){
				if (L[j]==a){
					L[j]=L[s];
				}
			}
		}
	}
	
	cin >> q;
	for (i=0;i<q;i++){
		cin >> s >> t;
		if (L[s]==L[t]){
			cout << "yes" <<endl;
		}else{
			cout << "no" <<endl;
		}
	}
	
	for (i=0;i<n;i++){
		cout << L[i] << endl;
	} 
	
	return 0;
}

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

vector<int> *v;
int *color;
int n;

void dfs(int i, int c){
        if(color[i]==c) return;
        color[i]=c;
        for(int j=0;j<v[i].size();j++)
                dfs(v[i][j], c);
}

void assignColor(){
        int c = 1;
        for(int i=0;i<n;i++){
                if(color[i]!=0) continue;
                dfs(i,c);
                c++;
        }

}

int main(){
        int m,q,a,b;
        cin>>n>>m;
        v = new vector<int>[n];
        color = new int[n];
        for(int i=0;i<m;i++){
                cin>>a>>b;
                v[a].emplace_back(b);
                v[b].emplace_back(a);
        }
        for(int i=0;i<n;i++) color[i] = 0;

        assignColor();

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

        return 0;
}