Go: package main

import (
	"bufio"
	"container/list"
	"os"
	"strconv"
	"fmt"
)

const (
	MAX = 100000
	NIL = -1
)

var (
	n     int
	G     [MAX][]int
	color [MAX]int
)

func DFS(r int, c int) {
	S := list.New()
	S.PushFront(r)
	color[r] = c
	for S.Len() != 0 {
		u := S.Remove(S.Front()).(int)
		for i := 0; i < len(G[u]); i++ {
			v := G[u][i]
			if color[v] == NIL {
				color[v] = c
				S.PushFront(v)
			}
		}
	}
}

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

func main() {
	var s, t, m, q int
	scanner := bufio.NewScanner(os.Stdin)
	scanner.Split(bufio.ScanWords)
	scanner.Scan()
	n, _ = strconv.Atoi(scanner.Text())
	scanner.Scan()
	m, _ = strconv.Atoi(scanner.Text())
	for i := 0; i < m; i++ {
		scanner.Scan()
		s, _ = strconv.Atoi(scanner.Text())
		scanner.Scan()
		t, _ = strconv.Atoi(scanner.Text())
		if i == 0 {
			G[s] = make([]int, 0)
			G[t] = make([]int, 0)
		}
		G[s] = append(G[s], t)
		G[t] = append(G[t], s)
	}

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

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

bool DFS(const vector<vector<int> >& G, int a, int b) {
    if (G[a].size() == 0) return false;

    stack<pair<int, int> > S;
    vector<bool> is_visited(G.size(), false);

    int idx = 0;
    do {
        if (idx >= G[a].size()) {
            a   = S.top().first;
            idx = S.top().second;
            S.pop();
            idx++;
            continue;
        }
        if (G[a][idx] == b) return true;
        if (!is_visited[G[a][idx]]) {
            is_visited[G[a][idx]] = true;
            S.push(make_pair(a, idx));
            a   = G[a][idx];
            idx = 0;
            continue;
        }
        idx++;
    } while (!S.empty());
    return false;
}


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

    vector<vector<int> > G(n);

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

// for (int i = 0; i < n; i++) {
//     cout << i << " : ";
//     for (int j = 0; j < G[i].size(); j++){
//         cout << G[i][j] << " ";
//     }
//     cout << endl;
// }



    int q;
    cin >> q;
    for (int i = 0; i < q; i++) {
        int a, b;
        cin >> a >> b;
        if (DFS(G, a, b)) {
            cout << "yes" << endl;
        } else {
            cout << "no"  << endl;
        }
    }
    return 0;
}

C++: #include <bits/stdc++.h>

using namespace std;

#define ll long long
typedef complex<double> P;

int main() {
  int n, m; cin >> n >> m;
  vector<int> adj[n];

  for (int i = 0; i < m; i++) {
    int v, u; cin >> v >> u;
    adj[v].push_back(u);
    adj[u].push_back(v);
  }

  int q; cin >> q;
  int sd[n] = {};

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

    queue<int> que;
    que.push(s);
    bool f = false;

    while(!que.empty()) {
      int v = que.front(); que.pop();
      if(v == t) {
        f = true;
        break;
      }

      for (int j = 0; j < n; j++) {
        if(find(adj[v].begin(), adj[v].end(), j) != adj[v].end() && sd[j] == 0) {
          que.push(j);
        }
      }
    }

    cout << (f ? "yes" : "no") << endl;

  }
}

C++: #include <iostream>
#include <vector>
using namespace std;
#define MAX_V 100000

int n, v, q;
vector<int> G[MAX_V];
bool visited[MAX_V];
int group[MAX_V];


void init(){
  for(int i = 0; i < v; i++){
    visited[i] = false;
    group[i] = -1;
  }
}

void dfs(int v, int g){
  group[v] = g;
  visited[v] = true;
  for(int i = 0; i < G[v].size(); i++){
    int to = G[v][i];
    if(!visited[to]){
      dfs(to, g);
    }
  }
}

int main(void){
  cin >> v >> n;
  for(int i = 0; i < n; i++){
    int from, to;
    cin >> from >> to;
    G[from].push_back(to);
    G[to].push_back(from);
  }
  init();
  for(int i = 0; i < v; i++){
    if(!visited[i]) dfs(i, i);
  }
  cin >> q;
  for(int i = 0; i < q; i++){
    int s, t;
    cin >> s >> t;
    if(group[s] != -1 && group[t] != -1 && group[s] == group[t]) cout << "yes" << endl;
    else cout << "no" << endl;
  }
  return 0;
}

C++: //Connected Component
#include <iostream>
#include <vector>

using namespace std;

static const int N = 100000;
int n, colors[N] = {};

void dfs(vector<vector<int>>  &G, int u, int c) {
    if(colors[u] != -1) return;
    colors[u] = c;
    for(auto v: G[u]) {
        dfs(G, v, c);
    }
}

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

    for(int i = 0; i < n; i++) colors[i] = -1;
    for(int i = 0; i < n; i++) {
        dfs(G, i, i);
    }

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

C++: #include <iostream>
#include<vector>
#include<stack>
using namespace std;
static const int MAXN=100000;
static const int NIL=-1;
 vector<int>G[MAXN];
 int color[MAXN];
 int n;
 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 b,q;
    cin>>n>>b;
    int s,t;
    for(int i=0;i<b;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;
}

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

#define MAX_N 100000
int par[MAX_N];//親の要素
int rank_[MAX_N];

//n要素で初期化
void init(int n)
{
	for (int i = 0; i < n; i++)
	{
		par[i] = i;
		rank_[i] = 0;
	}
}

//木の根を求める
int root(int x)
{
	if (par[x] == x)
	{
		return x;
	}
	else
	{
		return par[x] = root(par[x]);
	}
}

//xとyが同じ集合に属するか　否か
bool same(int x, int y)
{
	return root(x) == root(y);
}

//xとyの属する集合を併合
void unite(int x, int y)
{
	x = root(x);
	y = root(y);
	if (x == y)
	{
		return;
	}

	if (rank_[x] < rank_[y])
	{
		par[x] = y;
	}
	else
	{
		par[y] = x;
		if (rank_[x] == rank_[y])
		{
			rank_[x]++;
		}
	}


}

int main()
{
	int n;
	cin >> n;//頂点の数
	int m;
	cin >> m;//辺の数

	//初期化
	init(n);

	//木を作る
	for (int i = 0; i < m; i++)
	{
		int a, b;
		cin >> a >> b;
		if (same(a, b))
		{
			continue;
		}
		else
		{
			unite(a, b);
		}
	}

	int q;//クエリの数
	cin >> q;

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

	return 0;





}