Go: package main

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

//util
var sc = bufio.NewScanner(os.Stdin)

func nextStr() string {
	sc.Scan()
	return sc.Text()
}

func nextInt() int {
	sc.Scan()
	i, e := strconv.Atoi(sc.Text())
	if e != nil {
		panic(e)
	}
	return i
}

func printList(list []int) {
	n := len(list)
	buf := bufio.NewWriter(os.Stdout)
	for _, v := range list[0 : n-1] {
		buf.Write([]byte(fmt.Sprintf("%d ", v)))
	}
	buf.Write([]byte(fmt.Sprintf("%d\n", list[n-1])))
	buf.Flush()
}

func max(a, b int) int {
	if a > b {
		return a
	} else {
		return b
	}
}

func min(a, b int) int {
	if a > b {
		return b
	} else {
		return a
	}
}

//solve
const (
	MAX = 100000
	NIL = -1
)

var (
	n, m, q, s, t int
	G             [MAX][]int //連結リスト
	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)
			}
		}
	}
}

//幅優先探索で、頂点を色付け
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() {
	sc.Split(bufio.ScanWords)
	n, m = nextInt(), nextInt()
	for i := 0; i < m; i++ {
		s, t = nextInt(), nextInt()
		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()
	q = nextInt()
	for i := 0; i < q; i++ {
		s, t = nextInt(), nextInt()
		if color[s] == color[t] {
			fmt.Println("yes")
		} else {
			fmt.Println("no")
		}
	}

}

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

bool DFS(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);
// bool D[100000][100000];

    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 (set<int>::iterator it = G[i].begin(); it != G[i].end(); it++){
//         cout << *it << " ";
//     }
//     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 <stdio.h>
int ancestor[100000];
int find(int x){
    if(ancestor[x]==x)return x;
    return ancestor[x]=find(ancestor[x]);
}
int min(int a,int b){
    if(a<b)return a;
    return b;
}
int max(int a,int b){
    if(a>b)return a;
    return b;
}
int main(){
    int n,q,m,temp,x,y;
    scanf("%d%d",&n,&m);
    for(int i=0;i<n;i++)ancestor[i]=i;
    for(int i=0;i<m;i++){
        scanf("%d%d",&x,&y);
        temp=find(x);
        q=find(y);
        ancestor[max(temp,q)]=min(temp,q);
    }
    scanf("%d",&q);
    for(int i=0;i<q;i++){
        scanf("%d%d",&x,&y);
        if(find(x)!=find(y))printf("no\n");
        else printf("yes\n");
    }
}

C++: #include <iostream>
#include <vector>
#include <stack>
using namespace std;
static const int MAX = 100000;
static const int 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() 
{
    ios::sync_with_stdio(false);
    
    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(t);
    }

    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 <bits/stdc++.h>
using namespace std;

int n, m;

bool frend(vector<vector<int>> &M, vector<int> &memo, int i, int t) {
  if (memo[i] == 1) return false;
  int cnt = M[i].size();
  for (int z = 0; z < cnt; z++) {
    if (M[i][z] == t) return true;
    memo[i] = 1;
    if (frend(M, memo, M[i][z], t)) { return true; }
  }
  return false;
}

int main() {
  cin >> n >> m;
  vector<vector<int>> M(n);

  for (int i = 0; i < m; i++) {
    int id, f;
    cin >> id >> f;
    M[id].push_back(f);
    M[f].push_back(id);
  }
  int qn;
  cin >> qn;
  vector<vector<int>> q(qn, vector<int>(2));
  for (int i = 0; i < qn; i++) {
    cin >> q[i][0] >> q[i][1];
  }

  for (int i = 0; i < qn; i++) {
    vector<int> memo(n);
    bool res = frend(M, memo, q[i][0], q[i][1]);
    if (res) {
      cout << "yes" << endl;
    } else {
      cout << "no" << endl;
    }
  }
}

C++: #include <cstdio>

int parent[100001];

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

void Union(int a, int b)
{
  int pa = find(a);
  int pb = find(b);
  parent[pa] = pb;
}

int main()
{
  int n, m;
  scanf("%d%d", &n, &m);
  for (int i = 0; i < n; i++)
  {
    parent[i] = i;
  }
  while (m--)
  {
    int a, b;
    scanf("%d%d", &a, &b);
    Union(a, b);
  }
  int q;
  scanf("%d", &q);
  while (q--)
  {
    int a, b;
    scanf("%d%d", &a, &b);
    if (find(a) == find(b))
    {
      printf("yes\n");
    }
    else
    {
      printf("no\n");
    }
  }
}

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

struct node {
	std::vector<int> relation;
};

void dfs(std::vector<node> &n) {
	int d[100000];

	std::stack<int> s;
	for (size_t i = 0; i < n.size(); i++) {
		s.push(i);
		for (int k = 0; k < 100000; k++) {
			d[k] = 0;
		}
		while (s.size() != 0) {
			int num = s.top(); s.pop();
			d[num] = 1;
			for (std::vector<int>::iterator it = n[num].relation.begin(); it != n[num].relation.end(); it++) {
				if (d[*it] == 1) {
					n[num].relation.erase(it);
					it--;
				} else {
					s.push(*it);
					d[*it] = 1;
				}
			}
		}
	}
}

bool isconnect(std::vector<node> n, int from, int to) {
	std::stack<int> s;
	s.push(from);
	while(s.size() != 0) {
		from = s.top(); s.pop();
		for (std::vector<int>::iterator it = n[from].relation.begin(); it != n[from].relation.end(); it++) {
			if (to == *it) return true;
			s.push(*it);
		}
	}
	return false;
}

int main() {
	int people, relation;
	
	std::cin >> people >> relation;

	std::vector<node> n(people);

	for (int i = 0; i < relation; i++) {
		int from, to;
		std::cin >> from >> to;
		n[from].relation.push_back(to);
	}

	dfs(n);

	int question;
	std::cin >> question;

	for (int i = 0; i < question; i++) {
		int from, to;
		std::cin >> from >> to;
		if (isconnect(n, from, to)) {
			std::cout << "yes" << std::endl;
		} else {
			std::cout << "no" << std::endl;
		}
	}

	return 0;
}