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 <queue>

using namespace std;

const int kSize = 100001;

vector<int> adj[kSize];
bool isMarked[kSize];
int d[kSize];
int cc = 0;

void dfs(int v) {
    isMarked[v] = true;
    d[v] = cc;

    for (int i = 0; i < adj[v].size(); ++i) {
        int u = adj[v][i];
        if (!isMarked[u]) {
            dfs(u);
        }
    }
}

int main() {
    int n, m;
    fill(isMarked, isMarked + kSize, false);
    cin >> n >> m;
    for (int i = 0; i < m; ++i) {
        int from, to;
        cin >> from >> to;
        adj[from].push_back(to);
        adj[to].push_back(from);
    }

    for (int i = 0; i < n; ++i) {
        if (!isMarked[i]) {
            dfs(i);
            cc++;
        }
    }

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

C++: #include <iostream>
#include <vector>
#include <numeric>
#include <algorithm>
#include <unordered_set>

using namespace std;

const int N_MAX = 100000;
vector<vector<int32_t>> A(N_MAX);
vector<bool> visited(N_MAX);
vector<int32_t> deadend;

void dfs1(int32_t u) {
    visited[u] = true;

    for (int32_t v : A[u]) {
        if (!visited[v]) {
            dfs1(v);
        }
    }

    deadend.push_back(u);

    return;
}

unordered_set<int32_t> dfs2(int32_t u, unordered_set<int32_t> &scc) {
    visited[u] = true;

    for (int32_t v : A[u]) {
        if (!visited[v]) {
            dfs2(v, scc);
        }
    }

    scc.insert(u);

    return scc;
}

int main() {
    fill(visited.begin(), visited.end(), false);

    int32_t n, m;
    cin >> n >> m;

    for (int32_t i = 0; i < m; i++) {
        int32_t s, t;
        cin >> s >> t;

        A[s].push_back(t);
        A[t].push_back(s);
    }

    for (int32_t i = 0; i < n; i++) {
        if (!visited[i]) {
            dfs1(i);
        }
    }

    reverse(deadend.begin(), deadend.end());
    fill(visited.begin(), visited.end(), false);
    vector<unordered_set<int32_t>> sccs;

    for (int32_t u : deadend) {
        if (!visited[u]) {
            unordered_set<int32_t> scc;
            dfs2(u, scc);
            sccs.push_back(scc);
        }
    }

    int32_t q;
    cin >> q;

    for (int32_t i = 0; i < q; i++) {
        int32_t s, t;
        cin >> s >> t;

        bool flag = false;
        for (auto scc : sccs) {
            if (scc.find(s) != scc.end() && scc.find(t) != scc.end()) {
                flag = true;
                break;
            }
        }

        cout << (flag ? "yes" : "no") << endl;
    }

    return 0;
}