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<stack>
#include<vector>

using namespace std;

int n, color[100000];
vector<int> G[100000];

void dfs (int r, int c) {

    int i, u, v;

    stack<int> S;
    S.push(r);
    color[r] = c;

    while (!S.empty()) {
        u = S.top();
        S.pop();
        for (i = 0; i < G[u].size(); i++) {
            v = G[u][i];
            if (color[v] == -1) {
                color[v] = c;
                S.push(v);
            }
        }
    }

}

void assignColor () {

    int id = 1, i, u;

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

}

int main () { 

    int s, t, m, q, i;

    cin >> n >> m;

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

    assignColor ();

    cin >> q;

    for (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>

#define MAX 100000

int G[MAX][MAX];
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 <algorithm> //find

using namespace std;

#define N_MAX 100000

int search_connection(int s, int t);
vector<int> G[N_MAX], check_v;

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

    cin >> n >> m;

    //??£??\??????????????????
    for (i = 0; i < m; i++) {
        cin >> s >> t;
        G[s].push_back(t);
        G[t].push_back(s);
    }

    //??????????????????
    cin >> q;
    for (i = 0; i < q; i++) {
//        cout << "Q. " << i << endl;

        cin >> s >> t;

        if (check_v.size() != 0) check_v.clear();

        check_v.push_back(s);
        if ( search_connection(s, t) )
            cout << "yes" << endl;
        else
            cout << "no" << endl;
    }

    return 0;
}

int search_connection(int s, int t) {
    int i;
//    cout << "search " << s << ", " << t << endl;

    for (auto itr = G[s].begin(); itr != G[s].end(); itr++) {
        if (*itr == t) {
            return 1;
        }
        else if ( find(check_v.begin(), check_v.end(), *itr) != check_v.end() ) {
            //*itr?????¢?????¢?´¢??????node?????´??????????????¢?´¢????????????
        }
        else {
            //*itr???????????¢?´¢???????????????node?????´???
            check_v.push_back(*itr);
            if ( search_connection(*itr, t) )
                return 1;
        }
    }

    return 0;
}

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

#define MAX 100000

using namespace std;

int visited[MAX];
//adjacent list
vector<int> G[MAX];

//can go from s to t or not
bool ans;

void dfs(int s,int t){
  visited[s]=1;
  if(s==t) ans=true;
  for(int i=0;i<G[s].size();i++){
    if(visited[G[s][i]]==0){
      dfs(G[s][i],t);
    }
  }
}

int main(){
  int n,m; cin >> n >> m;
  for(int i=0;i<m;i++){
    int x,y; cin >> x >> y;
    G[x].push_back(y);
    G[y].push_back(x);
  }
  int q; cin >> q;
  for(int i=0;i<q;i++){
    for(int i=0;i<n;i++) visited[i]=0;
    ans=false;
    int s,t; cin >> s >> t;
    dfs(s,t);
    if(ans) cout << "yes" << endl;
    else cout << "no" << endl;
  }
}

C++: #include<iostream>
#include<vector>
#inlcude<stack>
using namespace std;
#define MAX 100000
#define NIL -1

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


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



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

int main() {

  int  m, i, j, v, s, t, q;

  cin >> n >> m;

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

  assignColor();

  cin >> q;

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

  return 0;

}

C++: #include<bits/stdc++.h>
using namespace std;
int par[100005];
int ra[100005];
void init(int n){
  for(int i=0;i<n;i++){
    par[i]=i;
    ra[i]=0;
  }
}
int find(int x){
  if(par[x]==x){
    return x;
  }
  else{
    return par[x]=find(par[x]);
  }
}
void unite(int x,int y){
  x=find(x);
  y=find(y);
  if(x==y)return;
  if(ra[x]<ra[y]){
    par[x]=y;
  }
  else{
    par[y]=x;
    if(ra[x]==ra[y])ra[x]++;
  }
}
bool same(int x,int y){
  return find(x)==find(y);
}

int main(){
  int n,m;
  cin >> n >> m;
  init(n);
  for(int i=0;i<m;i++){
    int a,b;
    cin >> a >> b;
    unite(a,b);
  }
  int q;
  cin >> q;
  for(int i=0;i<q;i++){
    int a,b;
    cin >> a >> b;
    if(same(a,b))cout << "yes" << endl;
    else cout << "no" << endl;
  }
  return 0;
}