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 <map>
#include <set>
#include <list>
#include <cmath>
#include <deque>
#include <queue>
#include <stack>
#include <cstdio>
#include <string>
#include <vector>
#include <complex>
#include <cstdlib>
#include <cstring>
#include <numeric>
#include <utility>
#include <iostream>
#include <algorithm>
#include <functional>
#include <unordered_map>
#include <unordered_set>

using namespace std;

#define ll long long
#define ull unsigned long long
#define INF (1 << 30)
#define LLINF (1LL << 62)
#define MOD7 1000000007
#define MOD9 1000000009
#define eps 1e-9
#define P pair<int, int>
#define pii pair<int, int>
#define pll pair<ll, ll>
#define pul pair<ull, ull>
#define all(a) (a).begin(), (a).end()
#define FOR(i,a,b) for (int i=(a);i<(b);++i)
#define RFOR(i,a,b) for (int i=(b)-1;i>=(a);--i)
#define REP(i,n) for (int i=0;i<(n);++i)
#define RREP(i,n) for (int i=(n)-1;i>=0;--i)

void YES() { cout << "YES" << endl; }
void NO() { cout << "NO" << endl; }
void Yes() { cout << "Yes" << endl; }
void No() { cout << "No" << endl; }
void yes() { cout << "yes" << endl; }
void no() { cout << "no" << endl; }

template<class T>
class UnDirectedGraph {
public:
	class Edge {
	public:
		int to;
		T cost;

		Edge(int t, T c) : to(t), cost(c) {}

		bool operator<(const Edge& right) const {
			return cost == right.cost ? to < right.to : cost < right.cost;
		}
	};

	vector<vector<Edge>> G;
	int V;

	UnDirectedGraph(int n = 0) {
		resize(n);
	}

	void resize(int n) {
		V = n;
		G.resize(n);
	}

	void addEdge(int from, int to, T cost = 0) {
		int v = max(from, to);
		if (v >= V)
			resize(v + 1);
		G[from].push_back(Edge(to, cost));
		G[to].push_back(Edge(from, cost));
	}

	vector<int> visit;
	int col = 0;
	void dfs(int s) {
		//vector<int> visit(V);
		visit.resize(V);
		col++;
		calcDfs(visit, s);
	}

	void calcDfs(vector<int>& visit, int s) {
		if (visit[s])
			return;

		//visit[s] = 1;
		visit[s] = col;
		for (int i = 0; i < G[s].size(); ++i) {
			calcDfs(visit, G[s][i].to);
		}
	}

	vector<int> bfs(int s) {
		vector<int> dist(V);
		queue<int> que;

		fill(dist.begin(), dist.end(), -1);
		dist[s] = 0;
		que.push(s);
		while (!que.empty()) {
			int from = que.front();
			que.pop();
			for (int i = 0; i < G[from].size(); ++i) {
				int to = G[from][i].to;
				if (dist[to] != -1)
					continue;
				dist[to] = dist[from] + 1;
				que.push(to);
			}
		}

		return dist;
	}
};

int main() {
	UnDirectedGraph<int> g;
	int n, m, from, to;
	cin >> n >> m;
	while (m--) {
		cin >> from >> to;
		g.addEdge(from, to);
	}
	
	for (int i = 0; i < n; ++i)
		g.dfs(i);

	int q;
	cin >> q;
	while (q--) {
		cin >> from >> to;
		if (g.visit[from] == g.visit[to])
			yes();
		else
			no();
	}

	return 0;
}

C++: #include<iostream>
#include<vector>
using namespace std;
static const int MAX = 100000;
static const int NIL = -1;

int n;
vector<int> G[MAX]; // List of vectors
int color[MAX];

void dfs_visit(int v, int id) {
    color[v] = id;
    for (int i=0; i<G[v].size(); i++) {
        int u = G[v][i];
        if (color[u]==NIL) {
            dfs_visit(u, id);
        }
    }
}

void dfs() {
    for (int v=0; v<n; v++) {
        color[v] = NIL;
    }
    int id = 0; // Cluster id
    for (int v=0; v<n; v++) {
        if (color[v]==NIL) {
            // If not clustered yet
            dfs_visit(v, 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);
    }

    dfs();

    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<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(){
  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<vector>
#inlcude<stack>
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;
  int i, v, u;
  S.push(r);
  color[r]=c;
  while (! S.empty()) {
    u=S.top();
    S.pop();
    for (i=0; i<G[u].size(); i++) {
        v=G[u][i];
      if (color[v]==NIL) {
        color[v]=c;
        S.push(v);
      }
    }
  }
}



void assignColor() {
  int i, u;
  int id=1;
  for (i=0; i<n; i++) color[i]=NIL;
  for (u=0; u<n; u++) {
    if (color[u]==NIL)
      dfs(u, id++);
  }
}

int main() {

  int  m, i, j, v, s, t, q;

  cin >> n >> m;

  for (i=0; i<m; i++) {
    cin >> s >> t;
    G[s].push_back(t);
    G[t].push_back(s);
  }

  assignColor();

  cin >> q;

  for (i=0; i<q; i++) {
    cin >> s >> t;
    if (color[s]== color[t]) {
      printf("yes\n");
    } else {
      printf("no\n");
    }
  }

  return 0;

}

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

std::vector<int> v[100010];
int n;
int m;

bool visited[10010];

bool dfs(int from, int to) {

  if(visited[to]) {
    return true;
  }

  visited[from] = true;
  for(int u=0; u<v[from].size(); ++u) {
    if(visited[v[from][u]]) continue;
    else {
      visited[v[from][u]] = true;
      dfs(v[from][u], to);
    }
  }

  return false;
}

int main() {
  std::cin >> n >> m;

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

  int q_n;
  std::cin >> q_n;
  bool answers[10010];
  for(int i=0; i<q_n; ++i) {
    int from, to;
    std::cin >> from >> to;
    for(int j=0; j<n; ++j) visited[j] = false;

    bool connected = dfs(from, to);
    answers[i] = visited[to];
  }

  for(int i=0; i<q_n; ++i) {
    if(answers[i]) std::cout << "yes" << std::endl;
    else std::cout << "no" << std::endl;
  }

}