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>

#define REP(i, n) for(int i=0;i<(int)(n);i++)
#define ALL(x) (x).begin(),(x).end()
const int INF = 1e9;

using namespace std;
int n, m;
struct node {
    int parent;
};

int main() {
    cin >> n >> m;
    node person[n];
    REP(i, n)
        person[i].parent = -1;
    REP(i, m){
        int s, t;
        cin >> s >> t;
        if(person[s].parent == -1){
            person[s].parent = s;
            person[t].parent = s;
        }
        else
            person[t].parent = person[s].parent;
    }
    int q;
    cin >> q;
    REP(i, q){
        int s, t;
        cin >> s >> t;
        if(person[s].parent != -1 && person[t].parent != -1  && person[s].parent == person[t].parent)
            cout << "yes" << endl;
        else
            cout << "no" << endl;
    }
    return 0;
}

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

const int MAX=100005;
vector<int> S[MAX];

int par[MAX];
int root(int a){
    if(par[a]==a) return a;
    else return par[a]=root(par[a]);
}
void unite(int a,int b){
    if(root(a)!=root(b)) par[root(b)]=root(a);
}
bool check(int a,int b){
    return root(a)==root(b);
}

int main(){

    int N,M;cin>>N>>M;
    for(int i=0;i<N;i++){
        par[i]=i;
    }
    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(check(a,b)) cout<<"yes"<<endl;
        else cout<<"no"<<endl;
    }

}

C++: #include <bits/stdc++.h>
#define ll long long
#define INF 999999999
#define MOD 1000000007

using namespace std;

typedef pair<int,int>P;

const int MAX_N = 100000;

int par[MAX_N];
int rank[MAX_N];

void initial(int n){		//?????????
	for(int i=0;i<n;i++){
		par[i] = i;
		rank[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(rank[x] < rank[y]){
		par[x] = y;
	}else{
		par[y] = x;
		if(rank[x] == rank[y])
			rank[x]++;
	}
}

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

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

C++: #include <cstdio>
#include <queue>
#include <vector>

std::queue<int> q;
typedef struct{
	bool isVisited;
	std::vector<int> neighbors;
} node;

void bfs(node* nodes, int t){
	int id;
	while (!q.empty()){
		id = q.front();
		q.pop();
		if (!nodes[t].isVisited){
			for (int i=0; i<nodes[id].neighbors.size(); i++){
				if (!nodes[nodes[id].neighbors[i]].isVisited){
					q.push(nodes[id].neighbors[i]);
					nodes[nodes[id].neighbors[i]].isVisited=true;
				}
			}
		}
	}
	if (nodes[t].isVisited) printf("yes\n");
	else printf("no\n");
}

int main(){
	int n, d, num_relation, n_query, s, t;
	node *nodes;

	scanf("%d %d", &n, &num_relation);
	nodes = new node[n];
	for(int i=0;i<num_relation;i++){
		scanf("%d %d", &s, &t);
		nodes[s].neighbors.push_back(t);
		nodes[t].neighbors.push_back(s);
	}

	scanf("%d", &n_query);
	for(int i=0;i<n_query;i++){
		for (int j=0; j<n;j++){
			nodes[j].isVisited=false;
		}
		scanf("%d %d", &s, &t);
		q.push(s);
		bfs(nodes, t);
	}

	delete []nodes;
	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 <iostream>#include <vector>#include <queue>static const int MAX=100000;using namespace std;vector<int> follow[MAX];int color[MAX];  //-1 represent No Visitedvoid bfs(int i,int c){    queue<int> Q;    Q.push(i);color[i]=c;    while(!Q.empty())    {        int p=Q.front();Q.pop();        for(int j=0;j<follow[p].size();j++)        {            if(color[follow[p][j]]!=-1) continue;            //else            Q.push(follow[p][j]); color[follow[p][j]]=color[p];        }    }}int main(){   int n,m;   cin>>n>>m;   for(int i=0;i<n;i++) color[i]=-1;   for(int i=0;i<m;i++)   {       int a,b;       cin>>a>>b;       follow[a].push_back(b);       follow[b].push_back(a);   }   int c=0;   for(int i=0;i<n;i++)   {       if(color[i]==-1)       {           bfs(i, c);           c++;       }   }   int order_num;cin>>order_num;   for(int i=0;i< order_num;i++)   {       int a,b;       cin>>a>>b;       if(color[a]==color[b]) cout<<"yes"<<endl;       else cout<<"no"<<endl;   }}

C++: #include <stdio.h>
#include <iostream>
#include <utility>
#include <algorithm>
#include <math.h>
#include <vector>
#include <list>
#define N 100000
using namespace std;
int n;
list<int> adj[N];
bool f[N] = {};

bool PathExists(int u, int v)
{
    f[u] = true;
    if (u == v)
        return true;
    while (!adj[u].empty())
    {
        if (!f[adj[u].front()] && PathExists(adj[u].front(), v))
            return true;
        adj[u].pop_front();
    }

    return false;
}

int main()
{
    int m, u, v, q;
    cin >> n >> m;

    for (int i = 0; i < m; i++)
    {
        cin >> u >> v;
        adj[u].push_back(v);
        adj[v].push_back(u);
    }

    cin >> q;
    for (int i = 0; i < q; i++)
    {
        cin >> u >> v;
        if (PathExists(u, v))
            printf("yes\n");
        else
            printf("no\n");
    }

    return 0;
}