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 <queue>
#include <set>
using namespace std;

const int MAX_N = 100000;

int G[MAX_N];
set<int> A[MAX_N];

void assign_gid(int user_num) {
  int gid;
  queue<int> Q;

  Q.push(0);
  G[0] = gid = 0;

  while (!Q.empty()) {
    int c = Q.front(); Q.pop();

    if (G[c] == -1) G[c] = ++gid;

    for (set<int>::iterator it = A[c].begin(); it != A[c].end(); it++) {
      if (G[*it] == -1) {
        G[*it] = gid;
        Q.push(*it);
      }
    }

    if (Q.empty()) {
      for (int i = 1; i < user_num; i++) {
        if (G[i] == -1) {
          Q.push(i);
          break;
        }
      }
    }
  }
}

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

  for (int i = 0; i < n; i++) G[i] = -1;

  for (int i = 0; i < m; i++) {
    int s, d; cin >> s >> d;
    A[s].insert(d);
    A[d].insert(s);
  }

  assign_gid(n);

  int q; cin >> q;

  for (int i = 0; i < q; i++) {
    int s, d; cin >> s >> d;
    if (G[s] == G[d]) cout << "yes";
    else cout << "no";
    cout << endl;
  }

  return 0;
}

C++: // -*- mode:c++; coding:utf-8; c-basic-offset:2; -*-
// ALDS1_11_D: Connected Components

#include <algorithm>
#include <climits>
#include <cstdio>
#include <vector>

using uint = unsigned int;

class Graph {
  std::vector<std::vector<uint>> g_;
  std::vector<uint> root_;
  
public:
  Graph(uint n)
  {
    g_.resize(n);
    root_.resize(n);
  }

  void add(uint from, uint to)
  {
    g_[from].push_back(to);
  }

  void setup()
  {
    std::fill(root_.begin(), root_.end(), UINT_MAX);
    for (auto i = 0u; i < g_.size(); ++i ) {
      dfs(i, i);
    }
  }

  bool reachable(uint from, uint to) const
  {
    return root_[from] == root_[to];
  }

private:
  void dfs(uint i, uint root)
  {
    if (root_[i] != UINT_MAX) return;
    root_[i] = root;
    for (auto j = 0u; j < g_[i].size(); ++j) {
      dfs(g_[i][j], root);
    }
  }
  
};

int main()
{
  uint n, m;
  std::scanf("%u %u", &n, &m);

  Graph g(n);

  uint s, t;
  for (auto i = 0u; i < m; ++i) {
    std::scanf("%u %u", &s, &t);
    g.add(s, t);
  }
  g.setup();

  uint q;
  std::scanf("%u", &q);
  for (auto i = 0u; i < q; ++i) {
    std::scanf("%u %u", &s, &t);
    std::puts(g.reachable(s, t) ? "yes" : "no");
  }
}

// eof

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

using namespace std;

static const int N = 100000;
static const int NIL = -1;

// 連結成分(Connected Components)

vector<int> G[N];
int color[N] = { NIL };

void depthFirstSeach(int u, int colorGroup)
{
    color[u] = colorGroup;
    //頂点vにつながっている頂点v
    for (int i = 0; i < G[u].size(); i++)
    {
        int v = G[u][i];
        if (color[v] == NIL)
            depthFirstSeach(v, colorGroup);
    }
}


int main(int argc, char *argv[])
{
    cin.tie(0);
    ios::sync_with_stdio(false);

    // 1行目は、ユーザー数n, 関係の数m
    int n, m;
    cin >> n >> m;
    // 2行目から、友達関係をm個
    for (int i = 0; i < m; i++)
    {
        int s, t; // sとtが友達
        cin >> s >> t;
        G[s].push_back(t);
        G[t].push_back(s);
    }

    // init color
    for (int i = 0; i < n; i++)
        color[i] = NIL;

    int colorGroup = 1;
    for (int u = 0; u < n; u++)
    {
        // 色がついていないノード(color=NIL)に色を付ける。
        // 深さ優先探索で、たどり着けるところまで色を付ける。
        // これをNILがなくなるまで続けることで色分けできる。
        if (color[u] == NIL) depthFirstSeach(u, colorGroup++);
    }

    // 質問の数q
    int q;
    cin >> q;
    for (int i = 0; i< q; i++)
    {
        int qs, qt; // qsからqtにたどり着けるか?
        cin >> qs >> qt;
        cout << ((color[qs] == color[qt]) ? "yes" : "no") << endl;
    }

    return 0;
}

C++: #include<stdio.h>
#include<queue>

#define MAX 100000

int G[MAX+1][MAX+1];
int n, m;
std::queue<int> Q;

//bool bfs(int src, int dest) {
//    bool C[MAX];
//    for (int i = 0; i < n; ++i) C[i] = false;
//
//    Q.push(src);
//    while(!Q.empty()) {
//        int cur = Q.front();Q.pop();
//        for (int i = 0; i < n; ++i) {
//            if (G[cur][i] == 0) continue;
//            if (C[i]) continue;
//            if (i == dest) return true;
//            Q.push(i);
//            C[i] = true;
//        }
//    }
//
//    return false;
//}

int main() {
    //scanf("%d %d", &n, &m);
    //for (int i = 0; i < n; ++i) {
    //    for (int j = 0; j < n; ++j) {
    //        G[i][j] = 0;
    //    }
    //}
    //for (int i = 0; i < m; ++i) {
    //    int u,k;
    //    scanf("%d %d", &u, &k);
    //    G[u][k] = 1;
    //    G[k][u] = 1;
    //}

    //int q;
    //scanf("%d", &q);
    //for (int i = 1; i <= q; ++i) {
    //    int s,d;
    //    scanf("%d %d", &s, &d);
    //    bfs(s, d) ? printf("yes\n") : printf("no\n");
    //}

    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(int r, int 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++) {
      int 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() {
  int 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;
}