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;
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;
    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");
        }
    }
}

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

using namespace std;
static const int MAX = 100005;
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 <bits/stdc++.h>
#define rep(i,a,b) for(int i=a;i<(b);++i)
#define erep(i,a,b) for(int i=a;i<=(int)(b);++i)
#define per(i,a,b) for(int i=(b);i>(a);--i)
#define eper(i,a,b) for(int i=((int)(a));i>=b;--i)
#define pb push_back
#define mp make_pair
#define INF 2000000000
#define MOD 1000000007
using namespace std;
typedef long long ll;
typedef pair<int,int> P;
int dy[]={0, 0, 1, -1};
int dx[]={1, -1, 0, 0};
int gcd(int a,int b){return b?gcd(b,a%b):a;}
int lcm(int a,int b){return a/gcd(a, b)*b;}

template <typename T> class union_find {
  vector<T> par, rank;

public:
  union_find(size_t n) {
    par.reserve(n + 1);
    rank.reserve(n + 1);
  }

public:
  void init(T n) { // add a set
    rep(i, 0, n) {
      par[i] = i;
      rank[i] = 0;
    }
  }

public:
  T find(T x) { // find the parent of x
    if (par[x] == x)
      return x;
    else
      return par[x] = find(par[x]);
  }

public:
  void unite(T x, T y) { // unite x and 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]++;
  }

public:
  bool same(T x, T y) { // compare x's parent and y's parent
    return find(x) == find(y);
  }
};

vector<int> x, y, p;
int main() {
 ios::sync_with_stdio ( false );
 cin.tie ( 0 );
    int n, m;
    cin >> n >> m;
    union_find<int> uf = union_find<int>(n+1);
    uf.init(n);
    rep(i, 0, n) {
        int t; cin >> t;
        p.pb(t);
    }
    rep(i, 0, m) {
        int val, a, b;
        cin >> a >> b;
        x.pb(a); y.pb(b);
        uf.unite(a, b);
    }
    int ans = 0;
    rep(i, 0, n) {
        if (uf.same(i+1, p[i])) ans++;
    }
    cout << ans << endl;
    return 0;
}

C++: #include<iostream>
#include<queue>
#include<vector>
#include<cstring>
using namespace std;
queue<int>Q; int x[200000], n, m, q, s, t; vector<int>a[200000];

bool bfs(int A,int B) {
	memset(x, 0, sizeof(x));
	x[A] = 1;
	Q.push(A);
	while (!Q.empty() || x[B] == 0) {
		for (int k = 0; k < a[Q.front()].size(); k++) {
			if (x[a[Q.front()][k]] == 0) { 
				Q.push(a[Q.front()][k]); x[a[Q.front()][k]] = 1; 
				a[A].push_back(a[Q.front()][k]);
			}
		}
		Q.pop();
	}
	if (x[B] == 1) {
		while (!Q.empty()) { Q.pop(); }
		return true;
	}
	else {
		return false;
	}
}

int main() {
	cin >> n >> m;
	for (int i = 0; i < m; i++) {
		cin >> s >> t;
		a[s].push_back(t);
		a[t].push_back(s);
	}
	cin >> q;
	for (int i = 0; i < q; i++) {
		cin >> s >> t;
		if (bfs(s, t)) { cout << "yes" << endl; }
		else { cout << "no" << endl; }
	}
	return 0;
}

C++: #include <iostream>
using namespace std;
  
int main() {
int d[100100];
int m,n,q;
cin>>n>>m;
for(int i=0;i<n;i++){
    d[i]=i;
}
for(int l=0;l<m;l++){
    int a,b;
    cin>>a>>b;
    int j ,h;
    j=a,h=b;
while(d[j]!=j && d[h]!=h){
    j=d[j];
    h=d[h];
}
if(d[j]==j){
	while(d[h]!=h){
		h=d[h];
	}
    d[j]=h;

    d[a]=h;
d[b]=h;
}
else{
	while(d[j]!=j){
		j=d[j];
	}
  d[h]=j;
    d[b]=j;
d[a]=j;
}
}
cin>>q;
for(int y=0;y<q;y++){
    int a,b;
    cin>>a>>b;
        int j ,h;
    j=a,h=b;
while(d[j]!=j && d[h]!=h){
    j=d[j];
    h=d[h];
}
if(d[j]==j){
	while(d[h]!=h){
		h=d[h];
	}}
else{
while(d[j]!=j){
		j=d[j];
	}
}

    if(j==h){
        cout<<"yes"<<endl;
    }
    else{
        cout<<"no"<<endl;
    }
}
    return 0;
}