Go: package main

import (
	"bufio"
	"container/list"
	"os"
	"strconv"
	"fmt"
)

const (
	MAX = 100000
	NIL = -1
)

var (
	n     int
	G     [MAX][]int
	color [MAX]int
)

func DFS(r int, c int) {
	S := list.New()
	S.PushFront(r)
	color[r] = c
	for S.Len() != 0 {
		u := S.Remove(S.Front()).(int)
		for i := 0; i < len(G[u]); i++ {
			v := G[u][i]
			if color[v] == NIL {
				color[v] = c
				S.PushFront(v)
			}
		}
	}
}

func assignColor() {
	id := 1
	for i := 0; i < n; i++ {
		color[i] = NIL
	}
	for i := 0; i < n; i++ {
		if color[i] == NIL {
			id++
			DFS(i, id)
		}
	}
}

func main() {
	var s, t, m, q int
	scanner := bufio.NewScanner(os.Stdin)
	scanner.Split(bufio.ScanWords)
	scanner.Scan()
	n, _ = strconv.Atoi(scanner.Text())
	scanner.Scan()
	m, _ = strconv.Atoi(scanner.Text())
	for i := 0; i < m; i++ {
		scanner.Scan()
		s, _ = strconv.Atoi(scanner.Text())
		scanner.Scan()
		t, _ = strconv.Atoi(scanner.Text())
		if i == 0 {
			G[s] = make([]int, 0)
			G[t] = make([]int, 0)
		}
		G[s] = append(G[s], t)
		G[t] = append(G[t], s)
	}

	assignColor()
	scanner.Scan()
	q, _ = strconv.Atoi(scanner.Text())
	for i := 0; i < q; i++ {
		scanner.Scan()
		s, _ = strconv.Atoi(scanner.Text())
		scanner.Scan()
		t, _ = strconv.Atoi(scanner.Text())
		if color[s] == color[t] {
			fmt.Println("yes")
		} else {
			fmt.Println("no")
		}
	}
}

C++: #include<iostream>
#include<vector>
#include<stack>
using namespace std;
static const int N = 100000;
static const int NIL = -1;
int n;
vector<int> G[N];
int reach[N];
void dfs(int r, int c) {
    stack<int> S;
    S.push(r);
    reach[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 (reach[v] == NIL) {
                reach[v] = c;
                S.push(v);
            }
        }
    }
}
void assign() {
    int id = 1;
    for (int i = 0; i < n; i++) reach[i] = NIL;
    for (int u = 0; u < n; u++)
        if (reach[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);
    }
    assign();
    cin >> q;
    for (int i = 0; i < q; i++) {
        cin >> s >> t;
        if (reach[s] == reach[t]) cout << "yes" << endl;
        else cout << "no" << endl;
    }
    return 0;
}

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

void boo(int b[], int y[], int w, int m){
	for(int i = 0; i < m; i++){
		if(b[i] == w) {
			if(y[b[i + m]] != -1)
				y[b[i + m]] = 1;
		}
	}
	for(int i = m; i < m * 2; i++){
		if(b[i] == w) {
			if(y[b[i - m]] != -1)
				y[b[i - m]] = 1;
		}
	}
}

int foo(int a, int s, int b[], int m, int n){
	int z = 0, y[100100] = {}, k = 1;
	y[a] = 1;
	while(k){
		k = 0;
		for(int i = 0; i < n; i++){
			if(y[i] == -1) continue;
			else if(y[i] == 1){ 
				if(i == s){
					z = 1;
					k = 0;
					break;
				} else{
					k = 1;
					y[i] = -1;
					boo(b, y, i, m);
				}
			}
		}
	}
	return z;
	
}

int main(){
	int b[200100];
	int n, m, q, a, s;
	int i, j, k;
	cin>>n>>m;
	for(i = 0; i < m; i++){
		cin>>b[i]>>b[m + i];
	}

	cin>>q;

	for(i = 0; i < q; i++){
		cin>>a>>s;
		if(foo(a, s, b, m, n) == 1){
			cout<<"yes"<<endl;
		} else {
			cout<<"no"<<endl;
		}
	}
	
	return 0;
}

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 topId, int c) {
    stack<int> S;
    S.push(topId);
    color[topId] = 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 <stack>
#include <stdio.h>
#include <vector>

using namespace std;

#define NMAX 100000
#define NIL -1

int n;
stack<int> S;
vector<int> adj[NMAX + 1]; // 0-origin
int d[NMAX + 1];           // if visited
int c[NMAX + 1];           // color

int next_unvisited() {
    for (int i = 0; i < n; i++) {
        if (d[i] == 0)
            return i;
    }
    return NIL;
}

int next_unvisited_adj(int u) {
    vector<int>::iterator it;
    for (it = adj[u].begin(); it != adj[u].end(); it++) {
        if (d[*it] == 0)
            return *it;
    }
    return NIL;
}

void dfs() {
    int x; // start vertex;
    int round = 0;
    while ((x = next_unvisited()) != NIL) {
        d[x] = 1;
        c[x] = round;
        S.push(x);
        while (!S.empty()) {
            int u = S.top();
            int v = next_unvisited_adj(u);
            if (v != NIL) {
                if (d[v] == 0) {
                    d[v] = 1;
                    c[v] = round;
                    S.push(v);
                }
            } else {
                S.pop();
            }
        }
        round++;
    }
}

int main() {
    int m, q, u, v;
    scanf("%d %d", &n, &m);
    for (int i = 0; i < m; i++) {
        scanf("%d %d", &u, &v);
        adj[u].push_back(v);
        adj[v].push_back(u);
    }
    for (int i = 0; i < n; i++)
        d[i] = 0;
    dfs();
    scanf("%d", &q);
    for (int i = 0; i < q; i++) {
        scanf("%d %d", &u, &v);
        if (c[u] == c[v])
            printf("yes\n");
        else
            printf("no\n");
    }
    return 0;
}

C++: // http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=ALDS1_11_A
// Graph I - Connected Components

#define SUBMIT

#include <utility>
#include <algorithm>
#include <iostream>
#include <iomanip>
#include <vector>
#include <limits>
#include <numeric>
#include <functional>
#include <set>
#include <cmath>
#include <cstring>
#include <climits>
#include <memory>

using namespace std;
using ui64 = unsigned long long;
using i64 = long long;

const int NIL = -1;
const ui64 MAX_N = 100000;

vector<int> adj[MAX_N];
int assigned_group_ids[MAX_N];
int n, m, q;
int group_id;

void dfs(int u, int id) {
    assigned_group_ids[u] = id;
    // search adj nodes
    for (const auto& v : adj[u]) {
        if (assigned_group_ids[v] == NIL) dfs(v, id);
    }
}

void assign_group() {
    memset(assigned_group_ids, NIL, sizeof(assigned_group_ids));
    group_id = 0;

    for (int u = 0; u < n; ++u) {
        if (assigned_group_ids[u] == NIL) {
            dfs(u, group_id);
            group_id++;
        }
    }
}

int main() {
    memset(adj, 0, sizeof(adj));
    cin >> n >> m;

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

    assign_group();

    cin >> q;

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

    return 0;
}