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<queue>
#include<vector>
#include<cstring>
using namespace std;
queue<int>Q; int x[200000], n, m, q, s, t; vector<int>a[100000];

bool bfs(int A,int B) {
	memset(x, 0, sizeof(x));
	x[A] = 1;
	while (!Q.empty()) {
		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; }
		}
	}
	if (x[B] == 1) {
		return true;
	}
	else {
		return false;
	}
}

int main() {
	cin >> n >> m >> q;
	for (int i = 0; i < m; i++) {
		cin >> s >> t;
		a[s].push_back(t);
		a[t].push_back(s);
	}
	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>
#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;
    int i, u, v;
    while ( !S.empty() ) {
        u = S.top();
        S.pop();
        for ( i = 0; i < G[u].size(); i++ ) {
            v = G[u][i];
            if ( color[v] == NIL ) {
                color[v] = c;
                S.push(v);
            }
        }
    }
}
 
void assignColor() {
    int id = 0;
    int i, u;
    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, i;
 
    cin >> n >> m;
 
    for ( i = 0; i < m; i++ ) {
        cin >> s >> t;
        G[s].push_back(t);
        G[t].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;
}