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 <cstdio>
#include <vector>

#define MAX 100000

#define WHITE 0
#define GRAY 1
#define BLACK 2


using namespace std;

vector<int> G[MAX];
int graphc[MAX];
int color[MAX];
int colorCount;

void def(int o)
{
	int v;

	for (int i = 0; i < G[o].size(); i++) {

		v = G[o][i];
		if (color[v] == WHITE) {

			color[v] = GRAY;
			def(v);
		}
	}
	color[o] = BLACK;
	graphc[o] = colorCount;
}


int main(void)
{
	int n;
	int m;
	int s;
	int t;
	int q;


	cin >> n >> m;

	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++) {

		if (color[i] == WHITE) {
			colorCount++;
			def(i);
			
		}
	}



	cin >> q;

	for (int i = 0; i < q; i++) {

		cin >> s >> t;

		cout << ((graphc[s] == graphc[t]) ? "yes" : "no" )<< endl;
	}

	return 0;
}

C++: #include<cstdio>
#include<vector>
#include<cstring>
#include<stack>
#include<iostream>
using namespace std;
int visited[100000]; int n;
vector<int> G[100000];

//void dfs_visit(int u)
//{
//  if(visited[u] == 1) return;
//  visited[u] = 1;
//  for(int i=0; i<G[u].size(); i++)
//  {
//    int v = G[u][i];
//    if(visited[v] == 0)
//      dfs_visit(v);
//  }
//}
//void dfs(int u, int v)
//{
//  memset(visited, 0, sizeof(n)*n);
//  dfs_visit(u);
//  if(visited[u] == visited[v])
//    printf("yes\n");
//  else printf("no\n");
//}  果然超时了哦。属实是弟弟行为哦~不过好歹能用哈哈哈。
void dfs_visit(int u, int id)
{
  if(visited[u] != 0) return;
  visited[u] = id;
  stack<int> s;//  诶~有意思。用stack来实现DFS一次把下层节点全压栈与一次压下层的一个节点仅仅是子节点的访问顺序颠倒了。
  s.push(u);
  while(!s.empty())
  {
    int v = s.top(); s.pop();
    for(int i=0; i<G[v].size(); i++)
    {
      int x = G[v][i];
      if(visited[x] == 0)
      {
        s.push(x);
        visited[x] = id;
      }
    }
  }
}
void dfs(int u)
{
  memset(visited, 0, sizeof(n)*n);
  int id = 1;// use id to denotes different circle so that all nodes can be visited by one bfs.
  for(int i=0; i<n; i++)
  {
    if(visited[i] == 0)
      dfs_visit(i, id++); // first circle id = 1, then 2 and so on ...
  }
}

int main()
{
  int m, q, u, v;
  scanf("%d%d",&n, &m);
  for(int i=0; i<m; i++)
  {
    scanf("%d%d", &u, &v);
    G[u].push_back(v);
    G[v].push_back(u);
  }
  scanf("%d", &q);
  dfs(0);
  for(int i=0; i<q; i++)
  {
    scanf("%d%d", &u, &v);
    if(visited[u] == visited[v])  printf("yes\n");
    else printf("no\n");
  }


  return 0;
}

C++: #include <iostream>
#include <cstdio>
#include <vector>
#include <queue>

using namespace std;

const int WHITE = 0, GREY = 1, BLACK = 2;

struct CC {
    int n;
    vector<vector<int>> g;
    vector<int> color;
    vector<int> component;
    int cId = 0; //component id
    
    CC (int n) : n(n) {
        g.assign(n, vector<int>(0));
        color.assign(n, WHITE);
        component.assign(n, -1);
    }
    
    void addEdge (int u, int v) {
        g[u].push_back(v);
        g[v].push_back(u);
    }
    
    void solve () {
        for (int i = 0; i < n; i++) {
            if (color[i] == WHITE) {
                cId++;
                bfs(i);
            }
        }
    }
    
    void bfs (int s) {
        queue<int> q;
        q.push(s);
        color[s] = GREY;
        component[s] = cId;
        while (!q.empty()) {
            int u = q.front();
            q.pop();
            for (int v : g[u]) {
                if (color[v] == WHITE) {
                    q.push(v);
                    color[v] = GREY;
                    component[v] = cId;
                }
            }
        }
    }
};

int main() {
    
    int n, m;
    cin >> n >> m;
    CC cc(n);
    
    for (int i = 0; i < m; i++) {
        int u, v;
        cin >> u >> v;
        cc.addEdge(u, v);
    }
    
    cc.solve();
    
    int q;
    cin >> q;
    for (int i = 0; i < q; i++) {
        int u, v;
        cin >> u >> v;
        if (cc.component[u] == cc.component[v]) {
            cout << "yes" << endl;
        }
        else {
            cout << "no" << endl;
        }
    }
    
    return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;
#define MAX 100000
#define 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(){
	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 <bits/stdc++.h>

using namespace std;
//int graph[100005][100005]; <-CompileError????????????????????????
vector<int> graph[100005];
int d[100005];
int color[100005];	
void bfs(int s, int n, int gpc){
	queue<int> Q;
	for(int i=0;i<n;i++){
		d[i] = 2e9;
	}
	color[s] = -1;
	d[s] = 0;
	Q.push(s);
	while(Q.size()!=0){
		int u = Q.front();
		Q.pop();
		for(int i=0;i<(int)graph[u].size();i++){
			int v = graph[u][i];
			if(color[v] == -2){
				color[v] = -1;
				d[v] = d[u] +1;
				Q.push(v);
			}
		}
		color[u] = gpc;
	}
}
void check(int n){
	int group = 0;
	for(int i=0;i<n;i++) color[i] = -2;
	for(int u=0;u<n;u++){
		if(color[u] == -2)bfs(u, n, group++);
	}
}

int main(){
	int n, m;
	cin >> n >> m;
	for(int i=0;i<m;i++){
		int num;
		int tmp;
		cin >> num >> tmp;
		graph[num].push_back(tmp);
		graph[tmp].push_back(num);
	}
	check(n);
	int q;
	cin >> q;
	for(int i=0;i<q;i++){
		int s, t;
		cin >> s >> t;
		if(color[s] == color[t]) cout << "yes"<<endl;
		else cout <<"no" << endl;
	}
}