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 <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() 
{
    ios::sync_with_stdio(false);
    
    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++: /**
 */

/*
 * test case 1
 2 1 1 2 1 1 2  
 test case 2
 4 4 1 2 1 3 2 4 3 4 1 1 2   
 */


#include <iostream>
#include <vector>
#include <queue>
using namespace std;
vector< vector<int> > rel;
vector<bool> visited;
int n, m, q;
int dest = 0;


bool fre1(int j) 
{
	for (int i=0;i<rel[j].size();i++)
	{
		int kk = rel[j][i];
		if (kk==dest) return true;
		if (visited[kk])continue;
		visited[kk]=true;
		if(fre1(kk))return true;
	}
	return false;
}

/**
 * preserve a priority que of nodes with the most connections. 
 * if there is a node with only 2 connections go look for the other one.
 */

priority_queue< pair<int, int> > pq;


bool fre3(int start) 
{
	for (int i=0;i<rel[start].size();i++)
	{
		int cand = rel[start][i];
		if (cand==dest) return true;
		if (visited[cand])continue;
		visited[cand]=true;
		int point = rel[cand].size();
		if (point == 1) continue;
		if (point == 2) {
			if (fre3(cand)) return true;
		} else {
			pq.push(pair<int, int>(point, cand));
		}
	}
	return false;
}


bool fre2(int start) 
{
	pq.push(pair<int,int>(0, start));
	while (pq.size())
	{
		pair<int, int> p = pq.top();
		pq.pop();
		start = p.second;
		if (fre3(start)) return true;
	}
	return false;
}


int main()
{
	cin >> n;
	rel.resize(n);
	cin >> m;
	for (int i=1;i<=m;i++){
		int j, k;
		cin >> j >> k;
		rel[j].push_back(k);
		rel[k].push_back(j);
	}

	cin >> q;
	for (int i=1;i<=q;i++){
		int start;
		cin >> start >> dest;
		visited.clear();
		visited.resize(n, false);
		cout << (fre2(start) ? "yes" : "no") << endl;
		while (pq.size()) pq.pop(); // forgot this.
	}

	return 0;
}

C++: #include <iostream>
#include <vector>
#include <algorithm>
#include <queue>
#include <map>
#include <set>
#include <math.h>
#include<cstring>
#include <cstdio>
using namespace std;
typedef long long int ll;
#define rep(i, a, n) for (ll i = a; i < (ll)(n); i++)
long long GCD(long long a, long long b) { return b ? GCD(b, a%b) : a; }
long long LCM(long long a, long long b)  {return a/GCD(a,b)*b;}
int n,m,q;
int st,en;
vector<int> G[100000];
int color[100000];
int cnt=0;
void dfs(int st,int cnt)
{
    color[st]=cnt;
    for(int i=0;i<G[st].size();i++)
    {
        if(color[G[st][i]]==-1)
        {
            dfs(G[st][i],cnt);
        }
    }
}
void makeColor()
{
    for(int i=0;i<n;i++)
    {
        if(color[i]==-1)
        {
            dfs(i,++cnt);
        }
    }
}
int main(){
    memset(color,-1,sizeof(color));
    cin>>n>>m;
    for(int i=0;i<m;i++)
    {
        int a,b;
        cin>>a>>b;
        G[a].push_back(b);
        G[b].push_back(a);
    }
    makeColor();
    cin>>q;
    
    for(int i=0;i<q;i++)
    {
        cin>>st>>en;
        if(color[st]==color[en])
            cout<<"yes"<<endl;
        else
            cout<<"no"<<endl;
    }
   return 0;
}

C++: #include <iostream>
#include <vector>
#include <queue>
#include <map>
using namespace std;

map<int, vector<int>> A;
int color[100001];

void assignColor(int u, int currentColor) {
    queue<int> Q;
    Q.push(u);
    color[u] = currentColor;
    int current;
    while(!Q.empty()) {
        current = Q.front();
        Q.pop();
        vector<int>::iterator it = A[current].begin();
        while(it != A[current].end()) {
            if (color[*it] == 0) {
                Q.push(*it);
                color[*it] = currentColor;
            }
            it++;
        }
    }
}

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

    int u1, u2;
    for (int i = 0; i < m; i++) {
        cin >> u1 >> u2;
        A[u1].push_back(u2);
        A[u2].push_back(u1);
    }

    for (int i = 0; i < n; i++) {
        color[i] = 0;
    }

    int c = 1;
    for (int i = 0; i < n; i++) {
        if (color[i] == 0) {
            assignColor(i, c);
            c++;
        }
    }

    int q, start, target;
    cin >> q;
    for (int i = 0; i < q; i++) {
        cin >> start >> target;

        if (color[start] == color[target]) {
            cout << "yes" << endl;
        } else {
            cout << "no" << endl;
        }
    }
}