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 <bits/stdc++.h>

using namespace std;

#define REP(i, n) for(int i = 0; i < n; i++)

int n, m;
vector<int> G[100000];
int id[100001];
int visit[100001] = {0};
int s, t;

void check(int x, int u) {
    visit[x] = 1;
    id[x] = u;

    int v;
    REP(i, G[x].size()) {
        v = G[x][i];
        if (visit[v] == 0) check(v, u);
    }
}

int main() {
    cin >> n >> m;
    int a, b;
    REP(i, m) {
        cin >> a >> b;
        G[a].push_back(b);
        G[b].push_back(a);
    }

    REP(i, n) {
        if (visit[i] == 0) check(i, i);
    }

    int q;
    cin >> q;
    REP(i, q) {
        cin >> s >> t;
        if (id[s] == id[t]) {
            cout << "yes" << endl;
        } else {
            cout << "no" << endl;
        }
    }

    REP(i, n) {
        cout << id[i] << endl;
    }
    return 0;
}

C++: #include <iostream>
#include <cstdio>
#include <climits>
#include <cmath>
#include <algorithm>
#include <utility>
#include <vector>
#include <string>
#include <stack>
#include <queue>
#define MAX 100000
#define INFTY 1<<30 // 2^30
using namespace std;
typedef long long llong;

static const int NIL = -1;

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

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

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

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

  assingColor();

  cin >> q;
  for(int i = 0; i < q; i++)
  {
    cin >> s >> t;
    cout << ((color[s] == color[t]) ? "yes" : "no") << endl;
  }
  return 0;
}

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

static const int MAX = 100000;
static const int WHITE = 0;
//static const int BLACK = 1;

vector<int> V[MAX];
//int n;
int color[MAX] = {0};

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

		}
	}
}

int main()
{
	int m,n;
	scanf("%d%d", &n, &m);
	int u,v;
	for(int i=0; i<m; i++)
	{
		scanf("%d%d", &u, &v);
		V[u].push_back(v);
		V[v].push_back(u);
	}

	int c = 1;
	for(int i=0; i<n; i++)
	{
		if(color[i] == WHITE)
			dfs(i,c++);
	}

	int q;
	scanf("%d", &q);
	for(int i=0; i<q; i++)
	{
		scanf("%d%d",&u,&v);
		if(color[u] == color[v])
			printf("yes\n");
		else
			printf("no\n");
	}

	return 0;
}

C++: #include <cstdint>
#include <vector>

using namespace std;

#define GRAPH_SIZE 100000

enum state_t {
  WHITE,
  GRAY,
  BLACK,
};

struct vertex_t {
  uint32_t color;
  vector<uint32_t> connections;
};

static vertex_t graph[GRAPH_SIZE];
static state_t state[GRAPH_SIZE];

static void colorize(uint32_t index, uint32_t color)
{
  if (state[index] == WHITE) {
    state[index] = GRAY;
    graph[index].color = color;
    for (uint32_t i = 0; i < graph[index].connections.size(); i++) {
      colorize(graph[index].connections[i], color);
    }
    state[index] = BLACK;
  }
}

void check_connection(size_t num)
{
  for (uint32_t i = 0; i < num; i++) {
    state[i] = WHITE;
  }

  uint32_t color = 1;
  for (uint32_t i = 0; i < knum; i++) {
    colorize(i, color);
    color++;
  }
}

#include <iostream>

int32_t main()
{
  uint32_t n, m;
  cin >> n >> m;

  for (uint32_t i = 0; i < m; i++) {
    uint32_t index, to;
    cin >> index >> to;
    graph[index].connections.push_back(to);
  }

  check_connection(n);

  uint32_t qs;
  cin >> qs;

  for (uint32_t i = 0; i < qs; i++) {
    uint32_t from, to;
    cin >> from >> to;

    if (graph[from].color == graph[to].color) {
      cout << "yes" << endl;
    } else {
      cout << "no" << endl;
    }
  }

  return 0;
}

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

//求解图的联通分量

using namespace std;

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

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

void dfs(int r, int c) {
    stack<int> S;
    S.push(r);

    color[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 (color[v] == NIL) {
                color[v] = c;
                S.push(v);
            }
        }
    }
}

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

    for (int u = 0; u < n; u++) {
        if (color[u] == NIL)
            dfs(u, id++);
    }
}

int main() {
    int s, t, m, q;

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

    assignColor();
    cin >> q;

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

    return 0;
}

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

using namespace std;

vector<set<int>> A;


bool dfs(int s, int t) {
    auto& S = A[s];
    if (S.find(t) != S.end()) {
        return true;
    }
    for (auto it = S.begin(); it != S.end(); ++it) {
        if (*it != t) {
            if (dfs(*it, t)) {
                return true;
            }
        }
    }
    return false;
}

int main() {
    int n;
    int m;
    cin >> n >> m;
    A.resize(n);
    for (int i = 0; i < m; ++i) {
        int s, t;
        if (s > t) {
            swap(s, t);
        }
        cin >> s >> t;
        A[s].insert(t);
        // A[t].insert(s);
    }

    int q;
    cin >> q;
    for (int j = 0; j < q; ++j) {
        int x, y;
        cin >> x >> y;

        if (dfs(x, y)) {
            cout << "yes";
        } else {
            cout << "no";
        }
        cout << endl;
    }

    return 0;
}