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 <algorithm>
#include <cmath>
#include <cstdio>
#include <deque>
#include <iostream>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <vector>

using namespace std;

typedef long long ll;

#define MOD 1000000007

vector<int> g[100000];
vector<bool> visit(100000);
vector<int> col(100000);
int c = 1;

void dfs(int v) {
  col[v] = c;
  visit[v] = true;
  for (auto u : g[v]) {
    if (!visit[u]) {
      dfs(u);
    }
  }
}

int main() {
  int n, m;
  cin >> n >> m;
  for (int i = 0; i < m; ++i) {
    int s, t;
    cin >> s >> t;
    g[s].push_back(t);
    g[t].push_back(s);
  }
  for (int i = 0; i < n; ++i) {
    if (!visit[i]) {
      dfs(i);
      c++;
    }
  }
  int q;
  cin >> q;
  for (int i = 0; i < q; ++i) {
    int s, t;
    cin >> s >> t;
    cout << (col[s] == col[t] ? "yes" : "no") << endl;
  }
  return 0;
}

C++: #include <iostream>

using namespace std;

const int N = 100000;
int A[N][N] = {{0}};
int n;

bool dfs(int s, int t) {
    if (A[s][t] == 1) {
        return true;
    }
    for (int i = 0; i < n; ++i) {
        if (i != t && A[s][i] != 0) {
            if (dfs(i, t)) {
                return true;
            }
        }
    }
    return false;
}

int main() {
    int m;
    cin >> n >> m;
    for (int i = 0; i < m; ++i) {
        int s, t;
        cin >> s >> t;
        A[s][t] = 1;
    }

    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;
}

C++: #include<stdio.h>

#define UNION_FIND_MAX_N (100010)
int union_find_par[UNION_FIND_MAX_N];
int union_find_rank[UNION_FIND_MAX_N];

void init(int n)
{
  int i;
  for(i=0;i<n;i++)
    {
      union_find_par[i]=i;
      union_find_rank[i]=0;
    }
}

int find(int x)
{
  if(union_find_par[x]==x)
    return x;
  else
    return union_find_par[x]=find(union_find_par[x]);
}

void unite(int x,int y)
{
  x=find(x);
  y=find(y);
  if(x==y)
    return;
  if(union_find_rank[x]<union_find_rank[y])
    union_find_par[x]=y;
  else
    union_find_par[y]=x;
  if(union_find_rank[x]==union_find_rank[y])
    union_find_rank[x]++;
}

int same(int x,int y)
{
  return find(x)==find(y);
}

int main()
{
  int n,m;
  int i;
  int a,b;
  int q;
  int s,t;
  scanf("%d %d",&n,&m);
  init(n);
  for(i=0;i<m;i++)
    {
      scanf("%d %d",&a,&b);
      unite(a,b);
    }
  scanf("%d",&q);
  for(i=0;i<q;i++)
    {
      scanf("%d %d",&s,&t);
      same(s,t)?puts("yes"):puts("no");
    }
  
  return 0;
}

C++: #include<iostream>
#include<string>
#include<algorithm>
#include<cstdio>
#include<vector>
#include<stack>

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

	scanf("%d%d", &n, &m);

	for (int i = 0; i < m; i++) {
		scanf("%d%d", &s, &t);
		G[s].push_back(t);
		G[t].push_back(s);
	}

	assignColor();

	scanf("%d", &q);

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

C++: #include<iostream>
#include<vector>
#include<stack>
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[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;
}

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

#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");
    }

}

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

int main()
{
 int i;
}