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<queue>

using namespace std;
queue<int>q;
vector<int>E[100005];
int d[100005],v[100005],n;
int id;
void bfs(int s,int id)
{
    d[s]=id;
    v[s]=true;
    q.push(s);
    while(!q.empty())
    {
        int u=q.front();q.pop();
        for(auto i:E[u])
        {
            if(!v[i])
            {
                v[i]=true;
                d[i]=id;
                q.push(i);
            }
        }
    }
}
int main()
{
    int m;
    cin>>n>>m;
    for(int i=0;i<m;i++)
    {
        int s,t;
        cin>>s>>t;
        E[s].push_back(t);
        E[t].push_back(s);
    }
    int q;cin>>q;
    id=1;
    for(int i=1;i<=n;i++)d[i]=-1;
    for(int i=1;i<=n;i++)
        if(d[i]==-1)
        bfs(i,id++);
    for(int i=0;i<q;i++)
    {
        int s,t;
        cin>>s>>t;
        if(d[s]==d[t])cout<<"yes"<<endl;
        else cout<<"no"<<endl;
    }
    return 0;
}

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

using namespace std;

// int d[10010];
int n, m;
vector<int> G[100010];
int reached[100010];
int color[100010];
int color_id = 0;

void bfs(int s, int color_id) {
  // cout << "--------------" << endl;
  // cout << "s:" << s << ", color:" << color_id <<endl;
  queue<int> Q;
  Q.push(s);
  while(!Q.empty()) {
    int u = Q.front(); Q.pop();
    // cout << "G[u].size():" << G[u].size() << endl;
    for (int i = 0; i < G[u].size(); i++) {
      // cout << u << "->" << G[u][i] << endl;
      if (reached[G[u][i]] == -1) {
        // cout << "reached at:" << G[u][i] << endl;
        Q.push(G[u][i]);
        reached[G[u][i]] = 1;
        color[G[u][i]] = color_id;
      }
    }
  }
}

void assignColor() {
  for (int i = 0; i < n; i++) {
    color[i] = -1;
  }

  for (int i = 0; i < n; i++) {
    if (color[i] == -1) {
      for (int j = 0; j < n; j++) {
        reached[j] = -1;
      }
      bfs(i, ++color_id);
    }
  }
}

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

  // 初期化
  for (int i = 0; i < m; i++) {
    cin >> s >> t;
    G[s].push_back(t);
    G[t].push_back(s);
  }
  // お絵かき
  assignColor();

  // 質問
  int q;
  cin >> q;
  // cout << "number of question:" << q << endl;
  for (int i = 0; i < q; i++) {
    cin >> s >> t;
    if (color[s] == -1 || color[t] == -1) {
      cout << "no" << endl;
    } else {
      if (color[s] == color[t]) {
        cout << "yes" << endl;
      } else {
        cout << "no" << endl;
      }
    }
  }
  // お絵かきの確認
  // cout << "----------" << endl;
  //
  // for (int i = 0; i < n; i++) {
  //   cout << i << ": " << color[i] << endl;
  // }

}

C++: #include<bits/stdc++.h>

using namespace std;

#define yes             cout << "yes\n"
#define no              cout << "no\n"
#define lop(n)          for(int i = 0; i < n; i++)
#define N               100009

int rep[N], n, m;

int findrep(int a)
{
    if(rep[a] == a)
        return a;

    return rep[a] = findrep(rep[a]);
}

void Union(int a, int b)
{
    rep[findrep(a)] = findrep(b);
}

int main()
{
    int u, v, q;

    cin >> n >> m;

    lop(n) rep[i] = i;

    lop(m)
    {
        cin >> u >> v;

        Union(u, v);
    }

    lop(n) u = findrep(i);

    cin >> q;

    lop(q)
    {
        cin >> u >> v;

        rep[u] == rep[v] ? yes : no;
    }

    return 0;
}

C++: #include <iostream>
#include <vector>
#include <stack>
using namespace std;
typedef long long ll;
static const ll MAX = 110000;
static const ll NIL = -1;

ll n;
vector<ll> G[MAX];
ll color[MAX];

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

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

int main() {
  ll s, t, m, q;
  cin >> n >> m;
  for (ll i = 0; i < m; i++) {
    cin >> s >> t;
    G[s].push_back(t);
    G[t].push_back(s);
  }

  assignColor();

  cin >> q;

  for (ll i = 0; i < q; i++) {
    if (color[s] == color[t]) {
      cout << "yes" << endl;
    }
    else {
      cout << "no" << endl;
    }
  }

  return 0;
}

C++: #include<iostream>
#include<vector>
using namespace std;

const int MAX = 100000, white = 0;
int n, colors[MAX], color = 0;
vector<int> G[MAX];

void dfs(int v){
    colors[v] = color;
    for (int i = 0; i < G[v].size(); i++)
    {
        if (colors[G[v][i]] == white)
        {
            dfs(G[v][i]);
        }
    }
}

void classification(){
    for (int i = 0; i < n; i++)
    {
        if (colors[i] == white)
        {
            color++;
            dfs(i);
        }
    }
}

int main(){
    int m, q;
    cin >> n >> m;
    for (int i = 0; i < m; i++)
    {
        int s, t;
        cin >> s >> t;
        G[s].emplace_back(t);
        G[t].emplace_back(s);
    }
    classification();
    cin >> q;
    for (int i = 0; i < q; i++)
    {
        int s, t;
        cin >> s >> t;
        if (colors[s] == colors[t])
        {
            cout << "yes" << endl;
        }
        else
        {
            cout << "no" << endl;
        }
    }
    
}

C++: #include<iostream>
#include<vector>
using namespace std;

vector<vector<int> >g;
int n,m,q,s,t;

vector<bool>visited;
vector<int>color;
void dfs(int s){
    for(int i=0;i<g[s].size();i++){
        if(color[g[s][i]]==-1){
            color[g[s][i]]=color[s];
            dfs(g[s][i]);
        }
    }
}
int main() {
    cin>>n>>m;
    g.resize(n);
    color.resize(n,-1);
    for(int i=0;i<m;i++){
        cin>>s>>t;
        g[s].push_back(t);
    }
    for(int i=0;i<n;i++){
        if(color[i]==-1){
            color[i]=i;
            dfs(i);
        }
    }
    cin>>q;
    for(int i=0;i<q;i++){
        cin>>s>>t;
        printf((color[s]==color[t]?"yes\n":"no\n"));
    }
    return 0;
}