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++: #define scanf_s scanf
#include <string>
#include <stdio.h>
#include <math.h>
#include <stack>
#include <queue>
#include <list>
#include <vector>
#include <iostream>
#include <algorithm>
using namespace std;

#define MAX 100
#define _MAX 1000
struct Graph
{
	int id, k = 0;
	list<int> node;
	int d = -1;
};
Graph G[MAX];
list<int> co;
int bo = false;
void Connect(Graph *g,Graph *f)
{
	if (g->k >= 0) {
		int a = true;
		co.push_back(g -> id);
		for (auto i = g->node.begin(); i != g->node.end(); ++i) {
			if (&G[*i] == f) { bo = true; return; }
			for (auto j = co.begin(); j != co.end(); ++j) {
				if (*j == *i) {
					a = false;
					break;
				}
			}
			if(a) return Connect(&G[*i], f);
			a = true;
		}
	}
}
int main(void)
{
	int n, m, q, a, b;
	int qq[_MAX] = { 0 };
	scanf_s("%d %d", &n, &m);
	for (int i = 0; i < m; ++i) {
		scanf_s("%d %d", &a, &b);
		G[a].id = a; G[b].id = b;
		++G[a].k; G[a].node.push_back(b);
		++G[b].k; G[b].node.push_back(a);
	}
	scanf_s("%d", &q);
	for (int i = 0; i < q; ++i) {
		scanf_s("%d %d", &a, &b);
		bo = 0;
		Connect(&G[a], &G[b]);
		qq[i] = bo;
		co.clear();
	}
	for (int i = 0; i < q; ++i) {
		if(qq[i]) printf("yes\n");
		else printf("no\n");
	}
}

C++: #include <iostream>
#include <string>
#include <cstring>
#include <fstream>
#include <cmath>
#include <iomanip>
#include <cstdlib>
#include <algorithm>
#include <vector>
#include <map>
#include <deque>
#include <map>
#include <set>
#include <queue>
#include <stack>
#include <list>
#include <unordered_map>

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(){
    

    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;
        }

    }

}

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

int n, m, q;
bool dp[100000];
vector<int> v[100000];

bool f(int s, int t) {
	if (!dp[s]) {
		if (s == t) {
			return true;
		}
		dp[s] = true;
		for (int i = 0; i < v[s].size(); i++) {
			if (f(v[s][i], t)) {
				return true;
			}
		}
	}
	return false;
}

int main(){
	int s, t;
	cin >> n >> m;
	for (int i = 0; i < m; i++) {
		cin >> s >> t;
		v[s].push_back(t);
		v[t].push_back(s);
	}
	cin >> q;
	for (int I = 0; I < q; I++) {
		cin >> s >> t;
		fill(dp, dp + n, false);
		if (f(s, t)) {
			cout << "yes" << endl;
		}
		else {
			cout << "no" << endl;
		}
	}

	return 0;
}

C++: #include <iostream>
#include <vector>
#include <stack>
#include <string>
#include <string.h>
using namespace std;
vector< vector<int> > v(100001);
//stack<int> st;
int n, m;
bool f[100001] = { false };

int main() {
	cin >> n >> m;
	for (int i = 0;i < m; i++) {
		int a, b; cin >> a >> b;
		v[a].push_back(b);
		v[b].push_back(a);
	}
	int q; cin >> q;
	vector<string> Ans(q);
	for (int i = 0; i < q; i++) {
		int s, t; cin >> s >> t;

		stack<int> st;
		st.push(s);
		while (!st.empty()) {
			int a = st.top(); st.pop();
			f[a] = true;
			if (a == t) { break; }
			for (int i = 0; i < v[a].size();i++) {
				if (f[v[a][i]] == false) {
					st.push(v[a][i]);
				}
			}
		}
		if (f[t] == true) { Ans[i] = "yes"; memset(f, false, n); }
		else { Ans[i] = "no"; memset(f, false, n); }
	
	}
	for (int i = 0; i < q;i++) {
		cout << Ans[i] << endl;
	}
	return 0;
}

C++: #include <iostream>
#include <vector>
#include <algorithm>
#include <numeric>
#include <queue>
#include <stack>
#include <map>
#define FOR(i,b,e) for(int i=b;i<e;i++)
#define REP(i,n) FOR(i,0,n)
using namespace std;

const int N = 100000;
int n, m, q;
vector< vector<int> > M;
bool V[N];

int bfs(int u, int v) {
  int s;
  queue<int> q;
  REP(i, n) V[i] = false;

  s = u;
  q.push(s);
  V[s] = true;

  while (!q.empty() && !V[v]) {
    s = q.front(); q.pop();
    REP(i, M[s].size()) {
      int t = M[s][i];
      if (!V[t]) {
        q.push(t);
        V[t] = true;
      }
    }
  }

  return V[v];
}

int main() {
	cin.tie(0);
 	ios::sync_with_stdio(false);

  cin >> n >> m;
  REP(i, n) {
    vector<int> vc;
    M.push_back(vc);
  }
  REP(i, m) {
    int u, v;
    cin >> u >> v;
    M[u].push_back(v);
    M[v].push_back(u);
  }

  cin >> q;
  REP(i, q) {
    int u, v;
    string answer;
    cin >> u >> v;
    answer = bfs(u, v) ? "yes" : "no";
    cout << answer << endl;
  }
}

C++: // ALDS1_11_D.cpp
// Graph I - Connected Components

#include <iostream>
#include <vector>
using namespace std;

bool isFriend(vector<vector<int>> &sns, vector<int> &arrived, int x, int y)
{
    if (sns[x][y] == 1) return true;
    bool res = false;
    arrived[x] = 1;
    for (int i = 0; i < sns.size(); i++) {
        if (sns[x][i] == 1 && !arrived[i]) {
            bool tmp = isFriend(sns, arrived, i, y);
            if (tmp) {
                res = true;
                break;
            }
        }
    }
    return res;
}

int main()
{
    int m, n, q;
    cin >> n >> m;
    vector<vector<int> > sns(n, vector<int>(n, 0));
    int x, y;
    for (int i = 0; i < m; i++) {
        cin >> x >> y;
        sns[x][y] = 1;
        sns[y][x] = 1;
    }

    cin >> q;
    while (q--) {
        vector<int> arrived(n);
        cin >> x >> y;
        bool res = isFriend(sns, arrived, x, y);
        if (res) cout << "yes" << endl;
        else cout << "no" << endl;
    }
    return 0;
}

C++: #include<iostream>
#include<queue>
#include<vector>
using namespace std;
#define MAX_N 500000
vector<int>X[MAX_N]; queue<int>Q;
int COLOR[MAX_N], N, M, Q1, A, B;
int main() {
	cin >> N >> M;
	for (int i = 0; i < M; i++) { cin >> A >> B; X[A].push_back(B); X[B].push_back(A); }
	int cnt = 0;
	for (int i = 0; i < N; i++) {
		if (COLOR[i] == 0) {
			Q.push(i); cnt++; COLOR[i] = cnt;
			while (!Q.empty()) {
				int a = Q.front(); Q.pop();
				for (int j = 0; j < X[a].size(); j++) {
					int to = X[a][j];
					if (COLOR[to] == 0) {
						COLOR[to] = cnt;
						Q.push(to);
					}
				}
			}
		}
	}
	cin >> Q1;
	for (int i = 0; i < Q1; i++) {
		cin >> A >> B;
		if (COLOR[A] == COLOR[B]) {
			cout << "1" << endl;
		}
		else {
			cout << "0" << endl;
		}
	}
	return 0;
}