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<bits/stdc++.h>

using namespace std;

int p[100010];

void init(int n)
{
    for(int i=0;i<n;i++)
    {
        p[i]=i;
    }
}

int fnd(int x)
{
    if(p[x]!=x)
    {
        p[x]=fnd(p[x]);
    }
    return p[x];
}

void unit(int a,int b)
{
    int fa=fnd(a),fb=fnd(b);

    if(fa!=fb)
    {
        p[fa]=fb;
    }
}

bool same(int a,int b)
{
    return fnd(a)==fnd(b);
}

int main()
{

    int n,m,q;

    cin>>n>>m;

    init(n);

    int a,b;
    for(int i=0;i<m;i++)
    {
        cin>>a>>b;
        unit(a,b);
    }

    cin>>q;

    for(int i=0;i<q;i++)
    {
        cin>>a>>b;

        if(same(a,b))
        {
            cout<<"yes"<<endl;
        }else
        {
            cout<<"no"<<endl;
        }
    }





    return 0;
}

C++: #include <iostream>
#include <vector>
#include <queue>
static const int MAX=100000;
using namespace std;

vector<int> follow[MAX];
int color[MAX];  //-1 represent No Visited

void bfs(int i,int c)
{
    queue<int> Q;
    Q.push(i);color[i]=c;
    while(!Q.empty())
    {
        int p=Q.front();Q.pop();
        for(int j=0;j<follow[p].size();j++)
        {
            if(color[follow[p][j]]!=-1) continue;
            //else
            Q.push(follow[p][j]); color[follow[p][j]]=color[p];
        }
    }
}

int main()
{
   int n,m;
   cin>>n>>m;
   for(int i=0;i<n;i++) color[i]=-1;
   for(int i=0;i<m;i++)
   {
       int a,b;
       cin>>a>>b;
       follow[a].push_back(b);
       follow[b].push_back(a);
   }
   int c=0;
   for(int i=0;i<n;i++)
   {
       if(color[i]==-1)
       {
           bfs(i, c);
           c++;
       }
   }
   int order_num;cin>>order_num;
   for(int i=0;i< order_num;i++)
   {
       int a,b;
       cin>>a>>b;
       if(color[a]==color[b]) cout<<"yes"<<endl;
       else cout<<"no"<<endl;
   }
}

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++){
    int v=g[u][i];
    if(color[v]==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;
}

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

using namespace std;

struct UnionFind
{
    vector<int> data;
    UnionFind() {}
 
    // initialize
    UnionFind(int size) : data(size, -1) {}
 
    void unite_set(int x, int y){
        x = root(x);
        y = root(y);
        bool is_unite = (x != y);
        
        if (is_unite){
            if (data[y] < data[x]){
                swap(x, y);
            }
            data[x] += data[y];
            data[y] = x;
        }
    }
 
    bool is_same(int x, int y){
        return root(x) == root(y);
    }
 
    int root(int x){
        return (data[x] < 0) ? x : data[x] = root(data[x]);
    }
 
    int size(int x){
        return -data[root(x)];
    }
};

int main()
{
    int n, q, m;
    int a, b;
    cin >> n;
    struct UnionFind d(n);
    vector<int> data;
    data.resize(n);
    
    for (int i=0; i<n; ++i){
        data[i] = i;
    }
    // unite
    cin >> m;
    for (int i=0; i<m; ++i){
        cin >> a >> b;
        d.unite_set(a, b);
    }
    // find
    cin >> q;
    for (int i=0; i<q; ++i){
        cin >> a >> b;
        if(d.is_same(a, b)){
            cout << "yes" << endl;
        }
        else {
            cout << "no" << endl;
        }
    }
}

C++: #include <iostream>
#include <stack>
#include <vector>
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 v, int id)
{
    stack<int> S;
    S.push(v);
    color[v] = id;
    int u;
    while (!S.empty()) {
        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] = id;
                S.push(v);
            }
        }
    }
}

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++);
        }
    }
}

int main(int argc, char const *argv[])
{
    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;
}

C++: #include<iostream>
#include<list>
#include<iterator>
#define MAX 100000
using namespace std;
char ans[MAX + 1];

class person
{
public:
	int id;
	bool Isdone = false;
	list <person*> lis;
	bool serch(person* Per)
	{
		if (ans[Per->id] == 1)return true;
		else if (ans[Per->id] == -1)return false;
		Isdone = true;
		for(list<person*>::iterator temp=lis.begin();temp!=lis.end();++temp)
		{
			if ((*temp) == Per)
			{
				ans[(*temp)->id] = 1;
				return true;
			}
			else if ((*temp)->Isdone == true)continue;
			else
			{
				if ((*temp)->serch(Per))
				{
					ans[(*temp)->id] = 1;
					return true;
				}
			}
		}
		ans[Per->id] = -1;
		return false;
	}
};

person P[MAX + 1];

int main()
{
	int n, m;
	cin >> n >> m;
	for (int i = 0; i < n; i++)P[i].id = i;
	for (int i = 0; i < m; i++)
	{
		int p1, p2;
		scanf("%d%d",&p1, &p2);
		P[p1].lis.push_back(&P[p2]);
		P[p2].lis.push_back(&P[p1]);
	}			 
	int q;
	cin >> q;
	for (int i = 0; i < q; i++)
	{
		int p1, p2;
		scanf("%d%d", &p1, &p2);
		if (P[p1].serch(&P[p2]))
		{
			cout << "yes" << endl;
		}
		else
		{
			cout << "no" << endl;
		}
		for (int l = 0; l < n; l++)P[l].Isdone = false;
		for (int l = 0; l < n; l++)ans[l] = 0;
	}
	return 0;
}