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<bits/stdc++.h>
using namespace std;
static const int MAX=100000;
static const int NIL=-1;
int n;
vector<int>G[MAX];//隣接リスト
int color[MAX];
void dfs(int r,int c){
  stack<int>S;
  S.push(r);
  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);
      }
    }
  }
}
int main(){
  int s,t,m,p;
  cin>>n>>m;
  for(int i=0;i<m;i++){
    cin>>s>>t;
    G[s].push_back(t);
    G[t].push_back(s);
  }
  int id=1;
  for(int i=0;i<n;i++){
    color[i]=NIL;
  }
  for(int i=0;i<n;i++){
    if(color[i]==NIL){
      dfs(i,id++);
    }
  }
  cin>>p;
  for(int i=0;i<p;i++){
    cin>>s>>t;
    if(color[s]==color[t]){
      cout<<"yes"<<endl;
    }else{
      cout<<"no"<<endl;
    }
  }
  return(0);
}

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

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){
    stack<int> ss {};
    ss.push(id);
    while(ss.size()){
        int p = ss.top();
        ss.pop();
        us[p].group = g;
        vector<int> fs = us[p].fs;
        for(auto x : fs){
            if(us[x].group == g){
                continue;
            }
            ss.push(x);
        }
    }
}

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<bits/stdc++.h>
using namespace std;
#define rp(i,j) for(long long i=0;i<j;i++)
#define rep(i,j,k) for(long long i=j;i<k;i++)
#define mod 1000000007
#define NIL -1
#define MAX 100000
typedef long long ll;
int n;
vector<int>a[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();
        rp(i,a[u].size()){
            int v=a[u][i];
            if(color[v]==NIL){
                color[v]=c;
                S.push(v);
            }
        }
    }
}
void colordefine(){
    int id=1;
    rp(i,n)color[i]=NIL;
    rp(i,n){
        if(color[i]==NIL)dfs(i,id++);
    }
}
int main(){
    int m,s,t,q;
    cin>>n>>m;
    rp(i,m){
        cin>>s>>t;
        a[s].push_back(t);
        a[t].push_back(s);
    }
    colordefine();
    cin>>q;
    rp(i,q){
        cin>>s>>t;
        string ans;
        if(color[s]==color[t])ans="yes";
        else ans="no";
        cout<<ans<<endl;
    }
}

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

const int NIL=-1;

int n, color[10000];
vector<int> G[100000];


void dfs(int v, int id){
    color[v]=id;

    for(int i=0; i<G[v].size(); i++){
        if(color[G[v][i]]==NIL) dfs(G[v][i],id);
    }
}

void assignColor(){
    int id=1;

    for(int i=0; i<n; i++) color[i]=NIL;
    for(int i=0; i<n; i++){
        if(color[i]==NIL){
            dfs(i,id); id++;
        }
    }
}

int main(void){
    int m; cin >> n >> m;

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

    assignColor();

    int q; cin >> q;
    for(int i=0; i<q; i++){
        int s,t; cin >> s >> t;
        if(color[s]==color[t]) printf("yes\n");
        else printf("no\n");
    }
}

C++: #include <iostream>
#include <stdio.h>
#include <cstring>
#include <math.h>
#include <algorithm>
#include <vector>
#include <string>
#include <stdlib.h>
#include <queue>
#include <stack>
#include <utility>
#define rep(i,n) for(int i=0;i<n;i++)
#define rrep(i,n) for(int i=n-1;i>=0;i--)
#define FOR(i,a,b) for(int i=a;i<b;i++)
#define ll long long
#define INF 1000000001
#define mod 1000000007
using namespace std;

int main(){
	int n,m;
	cin>>n>>m;
	vector<int> d(n);
	vector<vector<int>> g(n);
	int a,b;
	rep(i,m){
		//cin>>a[i]>>b[i];
		scanf("%d %d",&a,&b);
		g[a].push_back(b);
		g[b].push_back(a);
	}
	int q;
	cin>>q;
	vector<int> s(q),t(q);
	rep(i,q){
		//cin>>s[i]>>t[i];
		scanf("%d %d",&s[i],&t[i]);
	}
	rep(i,n){
		d[i]=0;
	}
	int check=1;
	int i=1;//???
	int i2=0;//???????????°
	while(check){
		stack<int> st;
		st.push(i2);
		d[i2]=i;
		while(!st.empty()){
			int x=st.top();
			st.pop();
			rep(j,g[x].size()){
				if(d[g[x][j]]==0){
					st.push(g[x][j]);
					d[g[x][j]]=i;
				}
			}
		}
		check=0;
		rep(j,n){
			if(d[j]==0){
				check=1;
				i++;
				i2=j;
				break;
			}
		}
	}

	rep(i,q){
		if(d[s[i]]==d[t[i]]){
			printf("yes\n");
		}else{
			printf("no\n");
		}
	}



	
}