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)
using ll = long long;
using P = pair<int, int>;

const int MAX = 100003;
vector<int> G[MAX];
int color[MAX];
int n;

void dfs(int s, int id) {
  stack<int> S;
  S.push(s);
  color[s] = id;

  while (!S.empty()) {
    int u = S.top(); S.pop();
    rep(i,G[u].size()) {
      int v = G[u][i];
      if (color[v] == -1) {
	color[v] = id;
	S.push(v);
      }
    }
  }
}

void assignColor() {
  int id = 1;
  memset(color, -1, sizeof(color));
  rep(u,n) {
    if (color[u] == -1) dfs(u, id++);
  }
}

int main() {
  int m, s, t;
  cin >> n >> m;
  rep(i,m) {
    cin >> s >> t;
    G[s].push_back(t);
    G[t].push_back(s);
  }

  assignColor();

  int q;
  vector<bool> ans;
  cin >> q;
  rep(i,q) {
    cin >> s >> t;
    if (color[s] == color[t]) ans.push_back(true);
    else ans.push_back(false);
  }
  rep(i,q) {
    cout << (ans[i] ? "yes" : "no") << endl;
  }
  return 0;
}

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

int n, m;

bool frend(vector<vector<int>> &M, vector<int> &memo, int i, int t) {
  if (memo[i] == 1) return false;
  for (int z = 0; z < M[i].size(); z++) {
    if (M[i][z] == t) return true;
    memo[i] = 1;
    if (frend(M, memo, M[i][z], t)) { return true; }
  }
  return false;
}

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

  for (int i = 0; i < m; i++) {
    int id, f;
    cin >> id >> f;
    M[id].push_back(f);
    M[f].push_back(id);
  }
  int qn;
  cin >> qn;
  vector<vector<int>> q(qn, vector<int>(2));
  for (int i = 0; i < qn; i++) {
    cin >> q[i][0] >> q[i][1];
  }

  for (int i = 0; i < qn; i++) {
    vector<int> memo(n);
    bool res = frend(M, memo, q[i][0], q[i][1]);
    if (res) {
      cout << "yes" << endl;
    } else {
      cout << "no" << endl;
    }
  }
}

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

using namespace std;

int main(){
	int n, m, s, t, q, i, j;
	int id;
	bool answer_yes = false;

	cin >> n >> m;
	vector< vector<int> > Adj(n);
	vector<int> Stack;
	vector<int> Check(n);
	vector<int>::iterator it, itend;

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

	/*for (i = 0; i < n; i++) {
		cout << "\n" << i << " : " << flush;
		for (auto it2 = Adj[i].begin(); it2 != Adj[i].end(); it2++) {
			cout << *it2 << " " << flush;
		}
	}
	cout << endl;*/

	cin >> q;
	for (i = 0; i < q; i++) {
		cin >> s >> t;
		
		// calculate
		Stack.push_back(s);
		Check[s] = true;
		while (!Stack.empty()) {
			id = Stack.back();
			//cout << "\nid : " << id << " stc : " << Stack.size() << endl;
			itend = Adj[id].end();
			for (it = Adj[id].begin(); it != itend; it++) {
				//cout << *it << " " << flush;
				if (!Check[*it]) {
					if (*it == t) {
						answer_yes = true;
						Stack.clear();
						break;
					}
					Stack.push_back(*it);
					Check[*it] = true;
					break;
				}
			}
			if (it == itend) {
				Stack.pop_back();
			}
		}
		if (answer_yes) {
			cout << "yes" << endl;
		} else {
			cout << "no" << endl;
			Stack.clear();
		}
		answer_yes = false;
		itend = Check.end();
		for (it = Check.begin(); it != itend; it++) {
			*it = false;
		}
	}
	
	return 0;
}

C++: 

#include<iostream>
#include<vector>
#include<stack>

using namespace std;


static const int MAX = 100'000;
static const int nil = -1;

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



void dfs(int r, int c) {
	stack<int> stk;
	stk.push(r);
	color[r] = c;

	while (!stk.empty())
	{
		int u = stk.top();stk.pop();

;		for (int i = 0; i < grp[u].size(); i++)
		{
			int v = grp[u][i];
			if (color[v] == nil) {
				color[v] = c;
				stk.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;
		grp[s].push_back(t);
		grp[t].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;
}