Go: package main

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

var (
	n     int
	G     [100000][]int
	color [100000]*int
)

func dfs(r int, c int) {
	S := Stack{}
	S.Push(r)
	color[r] = &c
	for !S.IsEmpty() {
		u := S.Pop()
		for i := 0; i < len(G[u]); i++ {
			v := G[u][i]
			if color[v] == nil {
				color[v] = &c
				S.Push(v)
			}
		}
	}
}

func assignColor() {
	id := 1
	for i := 0; i < n; i++ {
		color[i] = nil
	}
	for u := 0; u < n; u++ {
		if color[u] == nil {
			id++
			dfs(u, id)
		}
	}
}

func main() {
	sc := bufio.NewScanner(os.Stdin)
	sc.Split(bufio.ScanWords)
	sc.Scan()
	n, _ = strconv.Atoi(sc.Text())
	sc.Scan()
	r, _ := strconv.Atoi(sc.Text())

	for i := 0; i < r; i++ {
		sc.Scan()
		s, _ := strconv.Atoi(sc.Text())
		sc.Scan()
		t, _ := strconv.Atoi(sc.Text())
		G[s] = append(G[s], t)
		G[t] = append(G[t], s)
	}
	assignColor()
	sc.Scan()
	qNum, _ := strconv.Atoi(sc.Text())
	for i := 0; i < qNum; i++ {
		sc.Scan()
		s, _ := strconv.Atoi(sc.Text())
		sc.Scan()
		t, _ := strconv.Atoi(sc.Text())
		if color[s] == color[t] {
			fmt.Println("yes")
		} else {
			fmt.Println("no")
		}
	}
}

// Stack is Stack
type Stack struct {
	stack []int
}

// Push new value
func (stack *Stack) Push(val int) {
	stack.stack = append(stack.stack, val)
}

// Pop new value
func (stack *Stack) Pop() int {
	val := stack.stack[len(stack.stack)-1]
	stack.stack = stack.stack[0 : len(stack.stack)-1]
	return val
}

// IsEmpty return true when stack is empty
func (stack *Stack) IsEmpty() bool {
	return len(stack.stack) == 0
}

C++: #include <iostream>
#include <queue>
using namespace std;
struct Node{
    int u;
    vector<int> fri;
    bool flag;
};
queue<Node> refresh(queue<Node> que,Node node[],int n){
    while(!que.empty()){
        cout << que.front().u <<" \n";
        que.pop();
    }
    for(int i=0; i<n; i++)
        node[i].flag=false;

    return que;
}

int main(){
    int n,m,s,t;
    Node node[100000];
    cin >> n >> m;
    for(int i=0; i<n; i++)
        node[i].u=i;

    for(int i=0; i<m; i++){
        cin >> s >> t;

        node[s].fri.push_back(t);
        node[t].fri.push_back(s);
    }

    queue<Node> que;
    refresh(que,node,n);

    int q;
    cin >> q;

    bool answer[10000];
    for(int i=0; i<q; i++){
        answer[i]=false;
        cin >> s >> t;

        node[s].flag=true;
        que.push(node[s]);

        while(!que.empty() && !answer[i]){
         Node fro = que.front();

         for(int j=0; j<fro.fri.size(); j++){
            int x = fro.fri[j];
  
            if(x==t){
                answer[i]=true;
                break;
            }

            if(!node[x].flag){
                node[x].flag=true;
                que.push(node[x]);
            }
         }

          que.pop();
        }

        que=refresh(que,node,n);
    }

    for(int i=0; i<q; i++){
        if(answer[i])
            cout << "yes\n";
        else
            cout << "no\n";
    }
}

C++: #include<iostream>
using namespace std;
#include<vector>
#include<stack>
#define MAX 100000
int n,m;
vector<int>G[MAX];
stack<int>mp;
int color[MAX];

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

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

int main()
{
	cin >> n >> m;
	int x,y; 
	for (int i = 0; i < m ;i++){
		cin >> x >> y;
		G[x].push_back(y);
		G[y].push_back(x);
	}
	assignColor();
	cin >> m;
	for (int i = 0 ;i < m;i++){
		cin >> x >> y;
		if (color[x] == color[y]){
			cout << "yes" << endl;
		}
		else{
			cout << "no" << endl;
		}
	}
	return 0;
}

C++: #include <cmath>
#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <climits>
#include <map>
#include <list>
#include <stack>
#include <queue>
#include <vector>
#include <string>
#include <sstream>
#include <fstream>
#include <iostream>
#include <algorithm>
using namespace std;
 
struct node {
	int id;
	vector<int> rel;
};

node* nodes;

void dfs(int start, int cur, int* h){
	if(h[cur] == -1){
		h[cur] = start;
		for(int i = 0; i < nodes[cur].rel.size(); i++){
			dfs(start, nodes[cur].rel[i], h);
		}
	}
}

int main() {
	int n, m, q;
	scanf("%d %d", &n, &m);
	 
	nodes = new node[n];
	for(int i = 0; i < n; i++){
		nodes[i].id = i;
	}
	while(m--){
		int l, r;
		scanf("%d %d", &l, &r);
		nodes[l].rel.push_back(r);
		nodes[r].rel.push_back(l);
	}
	
	int *h = new int[n];
	for(int i = 0; i < n; i++){
		h[i] = -1;
	}
	for(int i = 0; i < n; i++){
		dfs(i, i, h);
	}
	
	scanf("%d", &q);
	while(q--){
		int l, r;
		scanf("%d %d", &l, &r);
		printf("%s\n", h[l]==h[r] ? "yes" : "no");
	}
	return 0;
}

C++: #include <iostream>
#include <cstdio>
#include <vector>
#define MAX_NODE 100000
#define MAX_EDGE 100000

using namespace std;

int n;//num of nodes
int e;//num of edges
int group[MAX_NODE+1];//0オリジン
int q;

bool neighbor_a[MAX_NODE+1];
vector<int> neighbor_v[MAX_NODE+1];//連接リスト

void addNeighbor(int num,int ori){//oriを含む連結グラフをつくる
	int ngb;
	
	for(int i = 0;i < neighbor_v[num].size();i++){//深さ優先探索
		if(neighbor_a[neighbor_v[num][i]] == false){
			neighbor_a[neighbor_v[num][i]] = true;
			neighbor_v[ori].push_back(neighbor_v[num][i]);
			ngb = neighbor_v[num][i];
			addNeighbor(ngb,ori);
		}
	}
}


int main(){
	int v_1,v_2;
	scanf("%d %d",&n,&e);

	for(int i = 0;i < e;i++){
		scanf("%d %d",&v_1,&v_2);
		neighbor_v[v_1].push_back(v_2);
		neighbor_v[v_2].push_back(v_1);
	}

	for(int i  = 0;i < n;i++) group[i] = -1;

	for(int i = 0;i < n;i++){
		if(group[i] != -1) continue;

		for(int j = 0;j < n;j++) neighbor_a[j] = false;//iの連接配列
		neighbor_a[i] = true;
		neighbor_v[i].push_back(i);

		addNeighbor(i,i);

		for(int j = 0;j < neighbor_v[i].size();j++) group[neighbor_v[i][j]] = i;

	}
	//for(int i = 0;i < n;i++) cout <<group[i] <<" ";
	//for(int i = 0;i < neighbor_v[5].size();i++) cout <<neighbor_v[5][i] <<" ";

	scanf("%d",&q);

	for(int i = 0;i < q;i++){
		scanf("%d %d",&v_1,&v_2);
		if(group[v_1] == group[v_2]) cout <<"yes" <<endl;
		else cout <<"no" <<endl;
	}
	return 0;
}

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

int n;
int parent[100000];
int r[100000]; //rank

//Union-find tree
void init(int n){
  for(int i = 0;i < n;i++){
    parent[i] = i;
    r[i] = 0;
  }
}

int find(int x){
  if(parent[x] == x) return x;
  else return parent[x] = find(parent[x]);
}

void unite(int x, int y){
  x = find(x);
  y = find(y);
  
  if(x == y) return ;
  
  if(r[x] < r[y]) parent[x] = y;
  else{
    parent[y] = x;
    if(r[x] == r[y]) r[x]++;
  }
}

bool same(int x, int y){
  return find(x) == find(y);
}

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

  //input
  cin >> n >> m;
  init(n);
  for(int i = 0;i < m;i++){
    cin >> s >> t;
    unite(s, t);
  }

  //ouptut
  cin >> q;
  for(int i = 0;i < q;i++){
    cin >> s >> t;
    if(same(s, t)) cout << "yes" << endl;
    else cout << "no" << endl;
  }
  
  return 0;
}