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<iostream>
#include<cstdlib>
#include<cstring>
#include<cstdio>
#include<vector>
#include<queue>
#include<stack>
#include<cmath>
#include<list>
#include<map>
#include<set>
using namespace std;

typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<string> VS;
typedef stack<int> SI;
typedef queue<int> QI;
typedef pair<int,int> PII;
typedef long long LL;

#define d(x)  cout<<#x<<" = "<<(x)<<endl;
#define c cout<<"#"<<endl;
#define ALL(a)  (a).begin(),(a).end()
#define RALL(a) (a).rbegin(), (a).rend()
#define PB push_back
#define MP make_pair
#define SZ(a) int((a).size())
#define EACH(i,c) for(typeof((c).begin()) i=(c).begin(); i!=(c).end(); ++i)
#define REACH(i,c) for(typeof((c).rbegin()) i=(c).rbegin(); i!=(c).rend(); ++i)
#define EXIST(s,e) ((s).find(e)!=(s).end())
#define SORT(c,n) sort(c,c+n)
#define VSORT(c) sort((c).begin(),(c).end())
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define REP(i,n)  FOR(i,0,n)
#define DFOR(i,b,a) for(int i=(b)-1;i>=(a);--i)
#define DREP(i,n) DFOR(i,n,0)
#define INF 2000000000

const double EPS = 1e-10;
const double PI  = acos(-1.0);
////////////////////////////////////////////////
VVI a;
int n,b,d[100010],p[100010];
QI q;
int main()
{
	//??£????????????????????????
	cin>>n>>b;
	REP(i,n+1)
	{
		a.push_back({0});
	}
	REP(i,b)
	{
		int s,t;cin>>s>>t;s++;t++;
		a[s][0]++;
		a[s].push_back(t);
		a[t][0]++;
		a[t].push_back(s);
	}
	FOR(i,1,n+1)
	{
		sort(&a[i][1],&a[i][a[i][0]+1]);
	}
	
	REP(i,n+1)p[i]=1,d[i]=0;
	d[1]=1;
	int g=1;
	for(q.push(1);SZ(q)!=0;)
	{
		int u=q.front();
		q.pop();
		if(a[u][0]==0)
		{
			d[u]=g;g++;
		}
		else
		{
			for(;p[u]<=a[u][0];)
			{
				int v=a[u][p[u]];p[u]++;
				if(v!=1&&d[v]==0)
				{
					d[v]=g;
					q.push(v);
				}
			}
		}
		if(q.empty())
		{
			int i;
			for(i=2;d[i]!=0;i++);
			if(i>n)
			{
				break;
			}
			else
			{
				g++;
				q.push(i);
			}
		}
	}
	cin>>n;
	REP(i,n)
	{
		int first,second;
		cin>>first>>second;first++;second++;
		if(d[first]==d[second])cout<<"yes"<<endl;
		else cout<<"no"<<endl;
	}
	return 0;
}

C++: #include<iostream>
#include<vector>
#include<stack>
using namespace std;
static const int MAX = 100000;
static const int NIL = -1;

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

int main() {
    
    int s, t, m, q;
    
    cin >> n >> m;
    
    for ( i = 0; i < m; i++ ){
        cin >> s >> t;
        G.push_back(t);
        G.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 <string.h>
#define N 100010
int father[N], root[N];
int findfather(int x){
    if(root[x]) return father[x];
    else return findfather(father[x]);
}
int main(){
    int n, m;
    scanf("%d %d", &n, &m);
    for(int i = 0; i < n; i++) {
        father[i] = i; root[i] = 1;
    }
    for(int k = 0; k < m; k++){
        int a, b;
        scanf("%d %d", &a, &b);
        root[b] = 0;
        father[b] = findfather(a);
    }
    int q;
    scanf("%d", &q);
    while(q--){
        int x, y;
        scanf("%d %d", &x, &y);
        if(father[x] == father[y]) printf("yes\n");
        else printf("no\n");
    }
    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 <stdio.h>
#include <stack>
#include <iostream>
using namespace std;
int G[100000][100000];
int vis[100000];
int n;

bool dfs(int s, int t)
{
    if (G[s][t] == 1 || G[t][s] == 1) return true;
    vis[s] = 1;
    for (int i = 0; i < n; i++)
    {
        if (G[s][i] == 1 && vis[i] == 0)
            {
                bool a = (dfs(i,t)||dfs(t,i)); 
                vis[s] = 0;
                return a;
            }

    } 
    vis[s] = 0;
    return false;
}

int main()
{
    //freopen("in3.txt","r",stdin);
    int m;
    scanf("%d %d",&n, &m);
    for (int i = 0; i < n; i++)
    {
        vis[i] = 0; 
    } 
    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 s, t;
        scanf("%d %d",&s,&t); 
        G[s][t] = 1;
        G[t][s] = 1;
    } 
    int q,s,t;
    scanf("%d",&q);
    for (int i = 0; i < q; i++)
    {
        scanf("%d %d",&s,&t);
        if(dfs(s,t)||dfs(t,s)) printf("yes\n");
        else printf("no\n");
    } 
    return 0;
}