Go: package main

import (
	"fmt"
)

var n, m int
var g [][]int
var color []int

func main() {
	fmt.Scan(&n, &m)
	g = make([][]int, n) // SNSの関係を表すグラフ
	for i := 0; i < m; i++ {
		var a, b int
		fmt.Scan(&a, &b)
		g[a] = append(g[a], b) // 無向重みなしグラフ
		g[b] = append(g[b], a)
	}
	color = make([]int, n) // 各ノードにつける色
	for i := 0; i < len(color); i++ {
		color[i] = -1 // 初期化しておく
	}
	type query struct {
		s, t int
	}
	var Q int
	fmt.Scan(&Q)
	qs := make([]query, Q)
	for i := 0; i < Q; i++ {
		fmt.Scan(&qs[i].s, &qs[i].t)
	}
	// fmt.Println("n", n, "m", m, "g", g, "Q", Q, "qs", qs)
	// 全ての頂点からdfsする
	id := 1
	for u := 0; u < n; u++ {
		if color[u] == -1 {
			dfs(u, id)
			id++
		}
	}
	// fmt.Println("color", color)
	for i := 0; i < Q; i++ {
		if color[qs[i].s] == color[qs[i].t] {
			fmt.Println("yes")
		} else {
			fmt.Println("no")
		}
	}
}

func dfs(v, c int) {
	// fmt.Printf("dfs(v %d, c %d) en:\n", v, c)
	color[v] = c
	for _, vv := range g[v] {
		// fmt.Printf("  v %d, g[v] %v, vv %d\n", v, g[v], vv)
		if color[vv] == -1 {
			dfs(vv, c)
		}
	}
}

C++: #include<cstdio>
#include<cstdlib>
#include<cstring>
#include<vector>
using namespace std;
//http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=ALDS1_11_D -- connected componenets
//method: check if their have the same component
//https://en.wikipedia.org/wiki/Connected_component_(graph_theory) -- connected component
//follow up : how cal the numbers of component--sorting the array and count
vector<int> neighbors[100005];
//why choose vector, not matrix
int root[100005];
//start is for the root
void dfs(int i, int start){
	root[i] = start;
	//visut all i's neighbors
	//c++ 11
	for(int j = 0; j< neighbors[i].size(); j++){
		int temp = neighbors[i].at(j);
		if(root[temp]==-1){
			dfs(temp,start);
		}
	}
}

int main(){
	int n,m,x,y,q;
	memset(root, -1, sizeof(root));
	scanf("%d %d",&n,&m);
	for(int i = 0; i<m; i++){
		scanf("%d %d",&x,&y);
		neighbors[x].push_back(y);
		neighbors[y].push_back(x);
	}
	for(int i = 0; i<n; i++){
		if(root[i]==-1){
			dfs(i,i);
		}
	}
	scanf("%d", &q);
	for(int i = 0; i<q; i++){
		scanf("%d %d",&x, &y);
		//printf("%d %d\n",root[x],root[y]);
		if(root[x] == root[y]){
			printf("yes\n");
		}else printf("no\n");
	}
	return 0;
}

C++: #define _CRT_SECURE_NO_DEPRECATE
#include <algorithm>
#include <cstdio>
#include <cstring>
#include <iostream>
#include <set>
#include <string>
#include <vector>
using namespace std;
typedef long long ll;
const int         N_MAX = 100000 + 2;
vector<int>       G[N_MAX];
int               n, m;
int               Q;
int               color[N_MAX];

void dfs(int v, int c) {
    color[v] = c;
    int size = G[v].size();
    for (int i = 0; i < size; i++) {
        int to = G[v][i];
        if (!color[to]) dfs(to, c);
    }
}

int main() {
    while (scanf("%d%d", &n, &m) != EOF) {
        memset(color, 0, sizeof(color));
        for (int i = 0; i < n; i++) {
            G[i].clear();
        }
        for (int i = 0; i < m; i++) {
            int from, to;
            scanf("%d%d", &from, &to);
            G[from].push_back(to);
            G[to].push_back(from);
        }
        int c = 1;
        for (int i = 0; i < n; i++) {
            if (!color[i]) {
                dfs(i, c);
                c++;
            }
        }

        scanf("%d", &Q);
        for (int i = 0; i < Q; i++) {
            int from, to;
            scanf("%d%d", &from, &to);
            if (color[from] == color[to])
                puts("yes");
            else
                puts("no");
        }
    }

    return 0;
}

C++: #include<iostream>
#include<cstdio>
#include<vector>
#include<queue>
#define Lens 100005

using namespace std;
int n, m, q;
vector<int> A[Lens];
queue<int>	Q;
char c[Lens], d[Lens];

int Find(int s, int t)
{
	Q.push(s);
	c[s] = 'g';
	while (!Q.empty())
	{
		s = Q.front();
		Q.pop();
		c[s] = 'g';
		for (int j = 0; j < A[s].size(); j++)
		{
			if (c[A[s][j]] == 'w')
				Q.push(A[s][j]);
			if (A[s][j] == t)
			{
				return 1;
			}
		}
	}
	return 0;
}

int main()
{
	cin >> n >> m;
	for (int i = 0; i < m; i++)
	{
		int s, t;
		cin >> s >> t;
		d[s] = d[t] = 'w';
		A[s].push_back(t);
		A[t].push_back(s);
	}
	cin >> q;
	for (int i = 0; i < q; i++)
	{
		while (!Q.empty())
			Q.pop();
		for (int j = 0; j < n; j++)
			c[j] = d[j];
		int s, t;
		cin >> s >> t;
		if (Find(s, t))
			cout << "yes" << endl;

		else
			cout << "no" << endl;
	}
	return 0;
}

C++: #include <iostream>
#include <algorithm>
#include <vector>
#include <stack>
#define MAX 100001
using namespace std;
vector<int> v[MAX];
int color[MAX];

void dfs(int x,int value){
	stack<int> s;
	s.push(x);
	color[x] = value;
	while(!s.empty()){
		int u = s.top();
		s.pop();
		for(int i = 0;i < v[u].size();i++){
			int a = v[u][i];
			if(color[a] == -1){
				color[a] = value;
				s.push(a);
			}
		}
	}
}

int main(){
	int n,m,q,x,y,value;
	cin >> n >> m;
	for(int i = 0;i < m;i++){
		cin >> x >> y;
		v[x].push_back(y);
		v[y].push_back(x);
	}

	value = 1;
	for(int i = 0;i < n;i++){
		color[i] = -1;
	}
	for(int i = 0;i < n;i++){
		if(color[i] == -1)dfs(i,value++);
	}

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

C++: #include <iostream>

using namespace std;

const int N = 100000;
int A[N][N] = {{0}};
int n;

bool dfs(int s, int t) {
    if (A[s][t] == 1) {
        return true;
    }
    for (int i = 0; i < n; ++i) {
        if (i != t && A[s][i] != 0) {
            if (dfs(i, t)) {
                return true;
            }
        }
    }
    return false;
}

int main() {
    int m;
    cin >> n >> m;
    for (int i = 0; i < m; ++i) {
        int s, t;
        cin >> s >> t;
        A[s][t] = 1;
    }

    int q;
    cin >> q;
    for (int j = 0; j < q; ++j) {
        int x, y;
        cin >> x >> y;

        if (dfs(x, y)) {
            cout << "yes";
        } else {
            cout << "no";
        }
        cout << endl;
    }

    return 0;
}

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

const int NIL=-1;
const int MAX=100000;

int n, color[MAX];
vector<int> G[MAX];

void dfs(int v, int id){
    stack<int> s;
    s.push(v);
    color[v]=id;

    while(!s.empty()){
        int u=s.top(); s.pop();
        for(int i=0; i<G[u].size(); i++){
            int v1=G[u][i];
            if(color[v1]==NIL){
                color[v1]=id;
                s.push(v1);
            }    
        }
    }
}

void assignColor(){
    int id=1;

    for(int i=0; i<n; i++) color[i]=NIL;
    for(int i=0; i<n; i++){
        if(color[i]==NIL){
            dfs(i,id); id++;
        }
    }
}

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

    for(int i=0; i<m; i++){
        int s,t; scanf("%d %d", &s, &t);
        G[s].push_back(t);
        G[t].push_back(s);
    }

    assignColor();

    int q; cin >> q;
    for(int i=0; i<q; i++){
        int s,t; scanf("%d %d", &s, &t);
        if(color[s]==color[t]) printf("yes\n");
        else printf("no\n");
    }

    return 0;
}