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<stdio.h>
using namespace std;

const int MAX = 100000;

int parent(int table[], int child) {
	if (table[child] == -1)return child;
	return table[child] = parent(table, table[child]);
}

int main() {
	int n, m, q;
	int table[MAX];

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

	for (int i = 0; i < n; i++)table[i] = -1;
	for (int i = 0; i < m; i++) {
		int s, t;
		scanf("%d %d", &s, &t);
		
		int ps = parent(table, s);
		int pt = parent(table, t);
		if (ps != pt) {
			table[ps] = pt;
		}
	}

	scanf("%d", &q);

	for (int i = 0; i < q; i++) {
		int s, t;
		
		scanf("%d %d", &s, &t);

		int ps = parent(table, s);
		int pt = parent(table, t);

		if (ps == pt) {
			printf("yes\n");
		}
		else {
			printf("no\n");
		}
	}
	return 0;
}

C++: #include <stdio.h>
#include <stack>
using namespace std;
int G[1000][1000];
int vis[100000];
int n;

bool dfs(int s, int t)
{
    if (G[s][t] == 1) return true;
    vis[s] = 1;
    for (int i = 0; i < n; i++)
    {
        if (G[s][i] == 1 && vis[i] == 0) return dfs(i,t); 
    } 
    //vis[s] = 0;
    return false;
}

int main()
{
    int m;
    scanf("%d %d",&n, &m);
    for (int i = 0; i < n; i++)
    {
        vis[i] = 0; 
    } 
    for (int i = 0; i < n; i++)
    {
        for (int j = 0; j < n; j++)
        {
            G[i][j] = 0; 
        }  
    } 
    for (int i = 0; i < m; i++)
    {
        int s, t;
        scanf("%d %d",&s,&t); 
        G[s][t] = 1;
        G[t][s] = 1;
    } 
    int q,s,t;
    scanf("%d",&q);
    for (int i = 0; i < q; i++)
    {
        scanf("%d %d",&s,&t);
        if(dfs(s,t)) printf("yes\n");
        else printf("no\n");
    } 
    return 0;
}

C++: #include<iostream>
#include<vector>
#include<stack>
#define MAX 100000
#define NIL -1

// 隣接リスト
std::vector<int> G[MAX];

// 隣接する頂点に同じ色を付けて記録するデータ
int color[MAX];

// 頂点数
int n;

// 深さ探索
// 探索した頂点には隣接頂点の印としてcの色を付ける
void dfs(int r, int c)
{
	std::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);
			}
		}
	}
}

// 色を付けて隣接頂点同士に分類する
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 m;
	std::cin >> n >> m;

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

	assignColor();

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

	return 0;
}

// 参考
// ALDS1_11_B_DepthFirstSearchと同じロジックで深さ探索を実装
void dfs_2(int r, int c)
{
	std::stack<int> S;
	S.push(r);
	color[r] = c;
	while (!S.empty())
	{
		int u = S.top();
		int v = -1;
		for (int i = 0; i < G[u].size(); i++)
		{
			if (color[G[u][i]] == NIL)
			{
				v = G[u][i];
			}
		}
		if (v != -1)
		{
			S.push(v);
			color[v] = c;
		}
		else
		{
			S.pop();
		}
	}
}

C++: #include <stdio.h>
#include <stack>
#include <vector> 
#include <iostream>
#define N 100000
using namespace std;

vector<int>  G[N];
int color[N];
int n;

void dfs(int s, int c)
{
    stack<int> st;
    color[s] = c;
    st.push(s);
    while(!st.empty())
    {
        int u = st.top();
        st.pop();
        for (int i = 0; i < G[u].size(); i++)
        {
            int v = G[u][i];
            if(color[v] == -1)
            {
                color[v] = c;
                st.push(v);
            }
        } 
    }
    return;
}

void assignColor()
{
    int id = 1;
    for (int i = 0; i < n; i++)
    {
        color[i] = -1;
    } 
    for (int u = 0; u < n; ++u)
    {
        if(color[u]==-1) dfs(u, id++);
    }

    return;
}

int main()
{
    //freopen("in3.txt","r",stdin);
    int m;
    scanf("%d %d",&n, &m);

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

    assignColor(); 

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