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 <stdio.h>
#include <stdlib.h>
#include <iostream>
#include <vector>
#include <stack>
#include <string.h>
#define rep(i, n) for(int i=0;i<n;i++)
#define NOT_FOUND 0
#define ENQUEUED 1
using namespace std;

vector<int> graph[100001];
int memo[100001];

int dfs(int start, int end) {
    if (start == end) {
        return 1;
    }
    memset(memo, NOT_FOUND, sizeof(memo));
    stack<int> stack;
    stack.push(start);
    memo[start] = ENQUEUED;

    while(!stack.empty()) {
        int v = stack.top();
        stack.pop();
        vector<int> edges = graph[v];

        rep(i, edges.size()) {
            int next = edges[i];
            if (next == end) {
                return 1;
            }
            if (memo[next] == NOT_FOUND) {
                memo[next] = ENQUEUED;
                stack.push(next);
            }
        }
    }
    return 0;
}

int main() {
    int n, m;
    cin >> n >> m;

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

    int q;
    cin >> q;

    for (int i = 0; i < q; i++) {
        int s, d;
        cin >> s >> d;
        if (dfs(s, d)) {
            cout << "yes" << endl;
        } else {
            cout << "no" << endl;
        }
    }
    return 0;
}

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

static const int N = 100000;
static const int NIL = -1;

int n;
vector<int> g[N];
int color[N];

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 assign_color(){
    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 m,s,t,q;
    cin >> n >> m;
    for(int i=0;i<m;i++){
        cin >> s >> t;
        g[s].push_back(t);
        g[t].push_back(s);
    }

    assign_color();

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

}

C++: #include<algorithm>
#include<bitset>
#include<cassert>
#include<cfloat>
#include<climits>
#include<cmath>
#include<deque>
#include<functional>
#include<iomanip>
#include<iostream>
#include<map>
#include<queue>
#include<set>
#include<stack>
#include<string>
#include<unordered_map>
#include<unordered_set>
#include<utility>
#include<vector>
#include<complex>
#include<list>
#include<cstdio>

#define REP(i, n) for(int i = 0;i < n;i++)
#define REPR(i, n) for(int i = n;i >= 0;i--)
#define FOR(i, m, n) for(int i = m;i < n;i++)
#define FORR(i, m, n) for(int i = m;i >= n;i--)
#define SORT(v, n) sort(v, v+n);
#define VSORT(v) sort(v.begin(), v.end());
#define llong long long
#define pb(a) push_back(a)


using namespace std;

typedef long long int ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;




const int INF = 1e9 + 7;


/******************************************************************************************/


//繋げる方向を一方向にする
typedef struct union_find {

	vector<ll> pa;//親
	vector<ll> ra;//木の深さ
	vector<ll> siz;
	//n要素で初期化
	void init(ll n) {
		pa.resize(n);
		ra.resize(n);
		siz.resize(n);
		for (ll i = 0; i < n; i++) {
			pa[i] = i;/*各ノードに番号を振る,この時par[x]=xとなる時は木の根となる*/
			ra[i] = 0LL;/*各ノード自体の高さは0*/
			siz[i] = 1LL;
		}
	}
	//木の根を求める
	ll find(ll x) {
		if (pa[x] == x) {
			return x;/*根ならそのノードの番号を返す*/
		}
		else {
			return pa[x] = find(pa[x]);/*根でないならさらにノードの根を探す*/
		}
	}

	//xとyの属する集合を併合する
	void unite(ll x, ll y) {
		x = find(x);//xの根の番号を探す
		y = find(y);//yの根の番号を探す
		if (x == y) {//一致すればつながっている
			return;
		}
		pa[y] = x;
		siz[x] += siz[y];
	}

	//xとyが同じ集合に属するか判定
	bool same(ll x, ll y) {
		return find(x) == find(y);//同じ集合なら1、違うなら0が返る
	}
}UF;

int main() {

	cin.tie(0);
	ios::sync_with_stdio(false);
	cout << fixed << setprecision(10);

	
	int n, m, q;

	cin >> n >> m;

	UF tree;
	tree.init(n+10);

	for (int i = 0; i < m; i++)
	{
		int a, b;
		cin >> a >> b;
		if (a > b) {
			swap(a, b);
		}
		//b→a
		tree.unite(a, b);

	}

	cin >> q;

	for (int i = 0; i < q; i++)
	{
		int a, b;
		cin >> a >> b;
		if (tree.same(a, b)) {
			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;
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,n)for(int i=0;i<n;i++)
using namespace std;

int par[100000],high[100000];
int find(int x){
	if(x==par[x])return x;
	return par[x]=find(par[x]);
}
void unite(int x,int y){
	x=find(x);y=find(y);
	if(x==y)return;
	if(high[x]>high[y]){
		par[y]=x;
	}
	else{
		par[x]=y;
		if(high[x]==high[y]){
			high[y]++;
		}
	}
}
int main(){
	int n,m;cin>>n>>m;
	rep(i,n){
		par[i]=i;
	}
	rep(i,m){
		int s,t;cin>>s>>t;
		unite(s,t);
	}
	int q;cin>>q;
	rep(i,q){
		int s,t;cin>>s>>t;
		puts(find(s)==find(t)?"yes":"no");
	}
}