Go: package main

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

// Node 頂点
type Node struct {
	gid  int   // グループID
	edge []int // 隣接辺
}

// NoID グループIDなし
const NoID = -1

// NewNode 頂点の生成
func NewNode() *Node {
	return &Node{gid: NoID, edge: []int{}}
}

func parseNode(nodes []*Node, gid int, queue []int) {
	if len(queue) == 0 {
		return
	}
	var nextQ []int
	for _, id := range queue {
		node := nodes[id]
		if node.gid == NoID {
			node.gid = gid
			for _, edge := range node.edge {
				nextQ = append(nextQ, edge)
			}
		}
	}
	parseNode(nodes, gid, nextQ)
	return
}
func digNode(nodes []*Node, id, gid int) {
	node := nodes[id]
	if node.gid != NoID {
		// 探索済み
		return
	}
	node.gid = gid
	for _, edge := range node.edge {
		digNode(nodes, edge, gid)
	}
	return
}

func main() {
	scanner := bufio.NewScanner(os.Stdin)
	n, m := eGetInt2(scanner)

	nodes := make([]*Node, n)
	for i := 0; i < n; i++ {
		nodes[i] = NewNode()
	}

	for i := 0; i < m; i++ {
		a, b := eGetInt2(scanner)
		nodes[a].edge = append(nodes[a].edge, b)
		nodes[b].edge = append(nodes[b].edge, a)
	}

	for i := 0; i < n; i++ {
		// 幅優先探索
		// gid := i
		// queue := []int{i}
		// parseNode(nodes, gid, queue)

		// 深さ優先探索
		digNode(nodes, i, i)
	}

	q := eGetInt(scanner)
	for i := 0; i < q; i++ {
		a, b := eGetInt2(scanner)
		if nodes[a].gid == nodes[b].gid {
			fmt.Println("yes")
		} else {
			fmt.Println("no")
		}
	}
}

func eGetInt(scanner *bufio.Scanner) int {
	t := eAtoi(strings.Fields(eGetline(scanner)))
	return t[0]
}
func eGetInt2(scanner *bufio.Scanner) (int, int) {
	t := eAtoi(strings.Fields(eGetline(scanner)))
	return t[0], t[1]
}

func eGetline(p *bufio.Scanner) string {
	if !p.Scan() {
		if err := p.Err(); err != nil {
			log.Fatal(err.Error())
		}
		return ""
	}
	return p.Text()
}

func eAtoi(s []string) []int {
	ints := make([]int, len(s))
	var err error
	for i, e := range s {
		ints[i], err = strconv.Atoi(e)
		if err != nil {
			log.Fatal(err.Error())
		}
	}
	return ints
}

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

using namespace std;

#define GRAPH_SIZE 100000

enum state_t {
  WHITE,
  GRAY,
  BLACK,
};

struct vertex_t {
  uint32_t color;
  vector<uint32_t> connections;
};

static vertex_t graph[GRAPH_SIZE];
static state_t state[GRAPH_SIZE];

static void colorize(uint32_t index, uint32_t color)
{
  if (state[index] == WHITE) {
    state[index] = GRAY;
    graph[index].color = color;
    for (uint32_t i = 0; i < graph[index].connections.size(); i++) {
      colorize(graph[index].connections[i], color);
    }
    state[index] = BLACK;
  }
}

void check_connection(size_t num)
{
  for (uint32_t i = 0; i < num; i++) {
    state[i] = WHITE;
  }

  uint32_t color = 1;
  for (uint32_t i = 0; i < num; i++) {
    colorize(i, color);
    color++;
  }
}

#include <iostream>

int32_t main()
{
  uint32_t n, m;
  cin >> n >> m;

  for (uint32_t i = 0; i < m; i++) {
    uint32_t index, to;
    cin >> index >> to;
    graph[index].connections.push_back(to);
    graph[to].connections.push_back(index);
  }

  check_connection(n);

  uint32_t qs;
  cin >> qs;

  for (uint32_t i = 0; i < qs; i++) {
    uint32_t from, to;
    cin >> from >> to;

    if (graph[from].color == graph[to].color) {
      cout << "yes" << endl;
    } else {
      cout << "no" << endl;
    }
  }

  return 0;
}

C++: #include <iostream>
using namespace std;
  
int main() {
int d[100100];
int m,n,q;
cin>>n>>m;
for(int i=0;i<n;i++){
    d[i]=i;
}
for(int l=0;l<m;l++){
    int a,b;
    cin>>a>>b;
    int j ,h;
    j=a,h=b;
while(d[j]!=j && d[h]!=h){
    j=d[j];
    h=d[h];
}
if(d[j]==j){
	while(d[h]!=h){
		h=d[h];
	}
    d[j]=h;
    d[a]=h;
d[b]=h;
}
else{
	while(d[j]!=j){
		j=d[j];
	}
  d[h]=j;
    d[b]=j;
d[a]=h;
}
}
cin>>q;
for(int y=0;y<q;y++){
    int a,b;
    cin>>a>>b;
        int j ,h;
    j=a,h=b;
while(d[j]!=j || d[h]!=h){
    j=d[j];
    h=d[h];
}
    if(j==h){
        cout<<"yes"<<endl;
    }
    else{
        cout<<"no"<<endl;
    }
}
    return 0;
}

C++: #include<bits/stdc++.h>
using namespace std;

vector<int> g[100000];
int c[100000],n;


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

void color(){
  int id=1;
  for(int i=0;i<n;i++) c[i]=-1;
  for(int i=0;i<n;i++){
    if(c[i]==-1) dfs(i,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);
  }
  color();
  cin>>q;
  for(int i=0;i<q;i++){
    cin>>s>>t;
    if(c[s]==c[t]) cout<<"yes"<<endl;
    else cout<<"No"<<endl;
  }
  return 0;
}

C++: #include <cstdio>
#include <cstdlib>
#include <cstring>

class queue{
    int head;
    int tail;
    int size;
    int *q;
public:
    queue(int n){
        head=0;
        tail=0;
        size=n;
        q = (int *)malloc(sizeof(int)*size);
    }
    void push(int n){
        if(tail-head>=size){
            return;
        }
//        printf("%d in.\n",n);
        q[tail%size]=n;
        tail++;
    }
    int pop(){
        if(tail<=head){
            return -1;
        }
        head++;
        return q[(head-1)%size];
    }
};

bool isFriend(int s, int t,int n,char **f,int *kakunin,int c){
    bool hoge;
    int tmp;
    queue ob(n);
    ob.push(s);
    kakunin[s]=c;
    for(int i=0;i<n;i++){
        hoge = true;
        while(true){
            tmp = ob.pop();
            if(tmp==-1)return false;
            for(int j=0;j<n;j++){
                if(f[tmp][j]&&(kakunin[j]<c)){
                    ob.push(j);
                    kakunin[j] = c;
                    f[s][j] = 1;
                    hoge = false;
                    if(j==t)return true;
                }
            }
        }
        if(hoge)return false;
    }
    return false;
}

int main(){
    int i,j,k,s,t,q,n,m;

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

    char **f = (char **)malloc(sizeof(char *)*n);
    int *kakunin = (int *)malloc(sizeof(int)*n);
    memset(kakunin,0,sizeof(int)*n);

    for(i=0;i<n;i++){
        f[i] = (char *)malloc(sizeof(char)*n);
        memset(f[i],0,sizeof(char)*n);
    }

    for(i=0;i<m;i++){
        scanf("%d %d",&s,&t);
        f[s][t] = 1;
        f[t][s] = 1;
    }

    scanf("%d",&q);
    for(i=0;i<q;i++){
        scanf("%d %d",&s,&t);
        if(isFriend(s,t,n,f,kakunin,i+1))printf("yes\n");
        else printf("no\n");
    }
    return 0;
}

C++: #include <iostream>
#include <vector>
#include <stack>
using namespace std;
#define MAX 100000
#define 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;
}