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 <cstdio>
#include <cctype>
#include <vector>
using namespace std;

#define si static inline
#define gcu getchar_unlocked
si int in() {
	int c, n = 0;
	//bool minus = false;
	//if ((c = gcu()) == '-') minus = true; else ungetc(c, stdin);
	while ((c = gcu()) >= '0' && c <= '9') n = 10 * n + (c - '0');
	return n; }
	//return minus ? -n : n; }
si void scan(char *s) {while (!isspace(*s++ = gcu()));}
#define pcu putchar_unlocked
#define svo si void out
template <typename T>
svo(T n) {
	static char buf[20];
	char *p = buf;
	//if(n < 0) pcu('-'), n *= -1;
	if (!n) *p++ = '0';
	else while (n) *p++ = n % 10 + '0', n /= 10;
	while (p != buf) pcu(*--p); }
svo(const char *s){while(*s)pcu(*s++);}
svo(char *s){while(*s)pcu(*s++);}
svo(char c){pcu(c);}
template <typename T>
//svo(vector<T> &v){for(T &x:v)out(' '),out(x);out('\n');}
svo(vector<T> &v){for(T &x:v)out(&x == &v[0]?"":" "),out(x);out('\n');}
template <typename head, typename... tail>
svo(head&& h, tail&&... t){out(h);out(move(t)...);}

struct union_find {
	struct node {int p, r = 0;};
	vector<node> nodes;

	union_find(int n) {
		nodes.resize(n);
		int i = 0;
		for (node &n: nodes)
			n.p = i++;
	}
	int find(int x) {
		int &p = nodes[x].p;
		if (p == x)
			return x;
		else {
			p = find(p);
			return p;
		}
	}
	void _union(int a, int b) {
		int ar = find(a), br = find(b);
		node &an = nodes[ar], &bn = nodes[br];
		if (an.r > bn.r)
			bn.p = ar;
		else if (an.r > bn.r)
			an.p = br;
		else if (ar != br) {
			bn.p = ar;
			an.r++;
		}
	}
	void read(int n) {
		int a;
		while(n--) {
			a = in();
			_union(a, in());
		}
	}
};

int main() {
	union_find u(in());
	u.read(in());
	int q = in();
	while (q--)
		out(u.find(in()) == u.find(in()) ? "yes" : "no", '\n');
}

C++: #include <iostream>
#include <string>
#include <vector>
#include <queue>
#include <algorithm>
#include <unordered_set>

using namespace std;

template<typename ISTREAM>
void readGraphListFromFriendInfo(ISTREAM& cin, vector< vector<int> >& friendGraphList) {
	size_t n;
	cin >> n;
	friendGraphList = vector< vector<int> >(n);
	size_t m;
	cin >> m;
	for (size_t i = 0; i != m; ++i) {
		size_t s,t;
		cin >> s >> t;
		friendGraphList.at(s).push_back(t);
		friendGraphList.at(t).push_back(s);
	}
	for (auto& v : friendGraphList)v.shrink_to_fit();
}

void accesibleNodeSearch(const vector<vector<int>>& graphList, vector<vector<int>>& visitMatrix, const int s, vector<bool>& visitList) {
	const size_t n = graphList.size();
	queue<int> nodeQueue;
	fill(visitList.begin(), visitList.end(), false);
	nodeQueue.push(s);
	visitList.at(s).flip();
	while (!nodeQueue.empty()) {
		const int id = nodeQueue.front();
		const vector<int>& adjList = graphList.at(id);
		for (const auto& adjID : adjList) {
			if (visitList.at(adjID))continue;
			const vector<int>& idList = graphList.at(adjID);
			if (find(idList.begin(), idList.end(), id) == idList.end())continue;
			nodeQueue.push(adjID);
			visitList.at(adjID).flip();
		}
		nodeQueue.pop();
	}
	const int num = count(visitList.begin(), visitList.end(), true);
	visitMatrix.at(s).reserve(num);
	for (int i = 0; i != n; ++i) {
		if (!visitList.at(i))continue;
		visitMatrix.at(s).push_back(i);
	}
}

void buildFriendAccesibility(const vector<vector<int>>& graphList, vector<vector<int>>& visitMatrix) {
	const int n = graphList.size();
	visitMatrix.resize(n, vector<int>());
	vector<bool> visitList(n);
	for (int i = 0; i != n; ++i) {
		accesibleNodeSearch(graphList, visitMatrix, i, visitList);
	}
}

template<typename T>
void execute(T& cin) {
	vector< vector<int> > graphList;
	readGraphListFromFriendInfo(cin, graphList);
	vector<vector<int>> visitMatrix;
	buildFriendAccesibility(graphList, visitMatrix);
	int q, s, t;
	cin >> q;
	for (int i = 0; i != q; ++i) {
		cin >> s >> t;
		cout << ( find(visitMatrix.at(s).begin(), visitMatrix.at(s).end(),t) != visitMatrix.at(s).end() ? "yes" : "no") << endl;
	}
}

int main()
{


	execute(cin);



	return 0;
}

C++: #include <algorithm>
#include <cstdio>
#include <iostream>
#include <map>
#include <queue>
#include <set>
#include <string>
#include <vector>

#define NMAX 100000
using namespace std;

struct Node {
  vector<int> friends;
};
int group[NMAX];

void bfs(vector<Node> &nodes, int id) {
  static int groupno = 1;
  queue<int> q;
  q.push(id);
  set<int> st;

  group[id] = groupno;

  while (!q.empty()) {
    int u = q.front();
    q.pop();
    for (int i = 0; i < nodes[u].friends.size(); i++) {
      int fid = nodes[u].friends[i];
      if (group[fid] == -1) {
        q.push(fid);
        group[fid] = groupno;
      }
    }
  }
  groupno++;
}

int main() {
  vector<Node> nodes;
  int nrel, nuser;

  cin >> nuser;
  cin >> nrel;
  nodes.resize(nuser);
  int tmp1, tmp2;
  for (int i = 0; i < nrel; i++) {
    cin >> tmp1 >> tmp2;
    nodes[tmp1].friends.push_back(tmp2);
    nodes[tmp2].friends.push_back(tmp1);
  }
  for (int i = 0; i < nodes.size(); i++) {
    group[i] = -1;
  }

  int q, s, t;
  cin >> q;

  for (int i = 0; i < q; i++) {
    scanf("%d%d", &s, &t);
    if (group[s] == -1)
      bfs(nodes, s);
    printf("%s\n", group[s] == group[t] ? "yes" : "no");
  }
}

C++: #include <iostream>
#include <vector>
#include <cstdio>
using namespace std;
int n,m;
vector <int> rel[100000];
int id[100001];
int visit[100001] = {0};
int s,t;


void check(int x, int u) { 
 visit[x] = 1;
  id[x] = u;

  int v ;
  for(int i=0;i<rel[x].size();i++) {
    v = rel[x][i];
    if(visit[v] == 0) {
      check(v,u);
    }
  }
}
    
  

int main() {

 

  cin >> n >> m;

 
  int a,b;


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


    cin >> a >> b;

    rel[a].push_back(b);
    rel[b].push_back(a);

  }
  
  for(int i =0;i<n;i++) {
    if(visit[i] == 0) {
      check(i,i);
    }
  }
  

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

  return 0;

}