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>
using namespace std;

vector<vector<int> > G;
vector<int> is_visited;
int b;

bool DFS(int a, int i) {
    if (a == b) return true;
    if (i >= G[a].size()) return false;
    is_visited[a] = 1;
    if (!is_visited[G[a][i]] && DFS(G[a][i], 0)) {
        return true;
    }
    return DFS(a, i + 1);
}

// bool DFS(const vector<vector<int> >& G,
//          vector<bool>& is_visited, int a, int b, int i) {
//     if (a == b) return true;
//     if (i >= G[a].size()) return false;
//     is_visited[a] = true;
//     if (!is_visited[G[a][i]] && DFS(G, is_visited, G[a][i], b, 0)) {
//         return true;
//     }
//     return DFS(G, is_visited, a, b, i + 1);
// }

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

    G.resize(n);
    is_visited.resize(n);

    for (int i = 0; i < m; i++) {
        int a, b;
        cin >> a >> b;
        G[a].push_back(b);
        G[b].push_back(a);
    }

// for (int i = 0; i < n; i++) {
//     cout << i << " : ";
//     for (int j = 0; j < G[i].size(); j++){
//         cout << G[i][j] << " ";
//     }
//     cout << endl;
// }



    int q;
    cin >> q;
    for (int i = 0; i < q; i++) {
        int a;
        cin >> a >> b;
        for (int j = 0; j < n; j++) {
            is_visited[j] = 0;
        }
        if (DFS(a, 0)) {
            cout << "yes" << endl;
        } else {
            cout << "no"  << endl;
        }
    }
    return 0;
}

C++: #include<iostream>
using namespace std;
#define MAX 101000

int ran[MAX], par[MAX];

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

int find(int x){
	return par[x] ==  x ? x : par[x] = find(par[x]);
}

void unite(int x, int y){
	x = find(x);
	y = find(y);
	
	if(x == y)return;
	
	if(ran[y] > ran[x]){
		par[x] = y;
	} else {
		par[y] = x;
		if(ran[y] == ran[x]) ran[x]++;
	}
}

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


int main(){
	int n, m, q, s, t;
	
	cin>>n>>m;
	
	init(n);
	
	for(int i = 0; i < m; i++){
		cin>>s>>t;
		unite(s,t);
	}
	
	cin>>q;
	
	for(int i = 0; i < q; i++){
		cin>>s>>t;
		cout<<(same(s,t)?"yes":"no")<<endl;
	}
	
	
	return 0;
}