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<stack>
#include<queue>
using namespace std;
const int MAXn=100000;
const int NIL=-1;

int n,col[MAXn];
vector<int> G[MAXn];

void dfs(int r,int c)
{
	stack<int> S;
	S.push(r);
	col[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(col[v]==NIL)
			{
				col[v]=c;
				S.push(v);
			}
		}
	}
	return;
}

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

int main() {
	int m,a,b,q;cin>>n>>m;
	for(int i=0;i<m;i++)
	{
		cin>>a>>b;
		G[a].push_back(b);
		G[b].push_back(a);
	}
	assigncol();
	cin>>q;
	for(int i=0;i<q;i++)
	{
		cin>>a>>b;
		if(col[a]==col[b])cout<<"yes"<<endl;
		else cout<<"no"<<endl;
	}
	return 0;
}

C++: #include <iostream>
#include <cstdio>
#include <vector>
#include <string>
#define N 100

void input_graph(std::vector<std::vector<int> >& g, int m){
    int s, t;
    for(int i=0; i<m; i++){//双連結リストを作る
        std::cin >> s >> t;
        g[s].push_back(t);
        g[t].push_back(s);
    }
}

void result(std::string ans[], int q){
    for(int i=0; i<q; i++){
        std::cout << ans[i] << '\n';
    }
}

void CC(std::vector<std::vector<int> >& g, std::string ans[], int q, int n){
    int s, t;
    int cnt = 0;
    std::vector<int> tmp;   //軌跡を保存
    //深さ優先探索
    while(cnt < q){
        //std::cout << "OK" << cnt << '\n';
        std::cin >> s >> t;
        int i = s;
        int nexti;
        int j;
        bool flag[n] = {false};
        bool f = false; //false:未到達 true:到達or終了
        while(!f){
            while(i != -1){
                //std::cout << "start\n";
                tmp.push_back(i);
                //std::cout << "i:" << i << '\n';
                flag[i] = true;
                //次の葉を探す
                if((int)g[i].size() != 0){//葉が最深でないとき
                    j = 0;
                    nexti = g[i][j];
                    while(flag[nexti]){
                        j++;
                        if(j == (int)g[i].size()){//葉がすべて探索済みなら
                            i = -1; //2つ目のwhile文を抜ける
                            break;
                        }
                        nexti = g[i][j];
                    }
                    if(i != -1){
                        if(nexti == t){
                            ans[cnt] = "yes";
                            i = -1;
                            f = true;
                            break;
                        }
                        i = nexti;
                    }
                }
                else{//葉が最深のとき
                    i = -1;
                }
            }
            if(!f){//まだ到達していなければ
                //ここから根に向かって戻る. 未探索の葉があればそちらへ行く
                //std::cout << "back\n";
                tmp.pop_back();
                i = (int)tmp.back();
                //std::cout << "i:" << i << '\n';
                tmp.pop_back();
                j = 0;
                nexti = g[i][j];
                while(flag[nexti]){
                    j++;
                    if(j == (int)g[i].size()){//現在のノードから未探索の葉がない
                        if((int)tmp.size() != 0){//まだtmpに軌跡が残っているなら
                            i = (int)tmp.back();
                            //std::cout << "i:" << i << '\n';
                            tmp.pop_back();
                            j = 0;
                            nexti = g[i][j];
                        }
                        else{//tmpに軌跡が残っていないなら
                            ans[cnt] = "no";
                            f = true;
                            break;
                        }
                    }
                }
            }
            i = nexti;
        }
        tmp.clear();    //一応clear
        cnt++;          //次のquestionへ
    }
}

int main(){
    int n, m;
    std::cin >> n >> m;
    std::vector<std::vector<int> > g;
    g.resize(n);
    input_graph(g, m);
    int q;
    std::cin >> q;          //質問数
    std::string ans[q];     //yes or no
    CC(g, ans, q, n);
    result(ans, q);
    return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;

void dfs(int in, int color,
    const vector<vector<int>>& graph,
    vector<int>& colors) 
{
    vector<bool> checkList(colors.size());
    stack<int> stack;
    stack.push(in);
    colors[in] = color;

    while (!stack.empty())
    {
        int x = stack.top();
        bool canLeave = true;
        for (const auto& g : graph[x]) {
            if (colors[g] == 0) {
                stack.push(g);
                colors[g] = color;
                checkList[g] = true;
                canLeave = false;
            }
        }
        if (canLeave) {
            stack.pop();
        }
    }
}

void wfs(int in, int color,
    const vector<vector<int>>& graph,
    vector<int>& colors)
{
    queue<int> queue;
    queue.push(in);
    vector<bool> checkList(colors.size());
    while (!queue.empty()) 
    {
        int x = queue.front();
        queue.pop();
        colors[x] = color;
        for (auto y : graph[x]) {
            if (!checkList[y]) {
                queue.push(y);
                checkList[y] = true;
            }
        }
    }
}

int main() {
    int n;
    int m;
    cin >> n >> m;
    vector<vector<int>> tree(n);
    vector<int> colors(n);

    for (int i = 0; i < m; ++i) {
        int s, t;
        cin >> s >> t;
        tree[s].push_back(t);
        tree[t].push_back(s);
    }
    int color = 0;
    for (int i = 0; i < n; ++i) {
        if (colors[i] != 0) {
            continue;
        }
        wfs(i, ++color, tree, colors);
        //dfs(i, ++color, tree, colors);
    }

    int qNum;
    cin >> qNum;
    vector<pair<int, int>> question(qNum);
    for (auto& q : question) {
        cin >> q.first >> q.second;
    }

    for (const auto& q : question) {
        if (colors[q.first] == colors[q.second]) {
            cout << "yes" << endl;
        }
        else {
            cout << "no" << endl;
        }
    }
}