Go: // AOJ ALDS1_11_D: http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=ALDS1_11_D

package main

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

var nocolor = -1

type graph struct {
	graph  [][]int
	colors []int
}

func nextInt(sc *bufio.Scanner) int {
	sc.Scan()
	v, _ := strconv.Atoi(sc.Text())
	return v
}

func newGraph(nodeNum int) *graph {
	colors := make([]int, nodeNum)
	g := make([][]int, nodeNum)
	for i := 0; i < nodeNum; i++ {
		g[i] = []int{}
		colors[i] = nocolor
	}

	return &graph{g, colors}
}

func constructGraph(sc *bufio.Scanner) *graph {
	usersNum := nextInt(sc)
	linkNum := nextInt(sc)

	g := newGraph(usersNum)
	for i := 0; i < linkNum; i++ {
		u := nextInt(sc) // node
		l := nextInt(sc) // link node
		// edge each other
		g.graph[u] = append(g.graph[u], l)
		g.graph[l] = append(g.graph[l], u)
	}
	return g
}

func (g *graph) dfs(r, color int) {
	g.colors[r] = color

	stack := list.New()
	stack.PushFront(r)

	for stack.Len() > 0 {
		v := stack.Remove(stack.Front()).(int)
		for _, u := range g.graph[v] {
			if g.colors[u] == nocolor {
				g.colors[u] = color
				stack.PushFront(u)
			}
		}
	}
}

func (g *graph) assignColor() {
	color := 1
	for u := 0; u < len(g.graph); u++ {
		if g.colors[u] == nocolor {
			g.dfs(u, color)
			color++
		}
	}
}

func (g *graph) isLink(s, t int) bool {
	return g.colors[s] == g.colors[t]
}

func main() {
	sc := bufio.NewScanner(os.Stdin)
	sc.Split(bufio.ScanWords)

	// construct graph and friendly colors
	g := constructGraph(sc)
	g.assignColor()

	// judge link
	q := nextInt(sc)
	for i := 0; i < q; i++ {
		s := nextInt(sc)
		t := nextInt(sc)

		if g.isLink(s, t) {
			fmt.Println("yes")
		} else {
			fmt.Println("no")
		}
	}
}

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

using namespace std;

struct UnionFind{
    UnionFind(int size):_array(size, -1){
    }

    bool same(int x, int y){
        return root(x) == root(y);
    }

    void unify(int x, int y){
        int rootx = root(x);
        int rooty = root(y);
        if( rootx == rooty ){
            return;
        }
        if( size(rootx) < size(rooty) ) swap(rootx,rooty);
        _array[rootx] += _array[rooty];
        _array[rooty] = rootx;
    }

    int root(int x){
        if( _array[x] < 0 ){
            return x;
        }
        return _array[x] = root(_array[x]);
    }

    int size(int x){
        return -_array[root(x)];
    }

    vector<int> _array;
};

void DFS(vector<vector<int>>& graph, int v, vector<int>& visited, int root, UnionFind& uf){
    visited[v] = true;
    uf.unify(v, root);
    for(int i = 0 ; i < graph[v].size(); i++){
        if(visited[graph[v][i]] == false){
            DFS(graph, graph[v][i], visited, root, uf);
        }
    }
}

int main(){
    int n, m;
    cin >> n >> m;

    vector<vector<int>> graph(n);
    for(int i = 0; i < m; i++){
        int v1, v2;
        cin >> v1 >> v2;
        graph[v1].push_back(v2);
        graph[v2].push_back(v1);
    }

    vector<int> visited(n, false);
    UnionFind uf(n);

    for(int i = 0; i < n ; i++){
        if( visited[i] == false ){
            DFS(graph, i, visited, i, uf);
        }
    }

    int q;
    cin >> q;

    for(int i = 0; i < q; i++ ){
        int v1, v2;
        cin >> v1 >> v2;
        if( uf.same(v1, v2) ){
            cout << "yes" << endl;
        }else{
            cout << "no" << endl;
        }
    }

    return 0;

}

C++: //TLEになってしまった

#include<iostream>
#include<vector>
#include<utility>
using namespace std;
#define INF 1000000000

void dfs(vector< vector<int> >& rel,vector<int>& v,int c,int k){
  int l=rel[k].size();
  for(int i=0;i<l;i++){
    if(v[rel[k][i]]==0){
      v[rel[k][i]]=c;
      dfs(rel,v,c,rel[k][i]);
    }
  }
}


int main(){
  int n,m;cin >> n >> m;
  vector<int> v(n,0);//番号を記録(訪問済みでない場合は0)
  vector< vector<int> > rel(n);//隣接リスト

  //隣接リスト、Nodeの行列を作る必要ない
  for(int i=0;i<m;i++){
    int x,y;cin >> x >> y;
    rel[x].push_back(y);rel[y].push_back(x);
  }

  int col=0;
  for(int i=0;i<n;i++){
    if(v[i]==0){
      col++;
      dfs(rel,v,col,i);
    }
  }

  int q;cin >>q;
  for(int i=0;i<q;i++){
    int s,t;cin >> s >> t;
    //非連結だと0だろ
    if(v[s]==0 or v[s]!=v[t]) cout << "no" << endl;
    else cout << "yes" << endl;
  }
  # if 0
  for(int i=0;i<n;i++){cout <<  v[i] << " ";}
  cout << endl;
  # endif
}