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<iostream>
#include<stack>
#include<vector>

using namespace std;

int n, color[10000];
vector<int> G[10000];

void dfs (int r, int c) {

    int i, u, v;

    stack<int> S;
    S.push(r);
    color[r] = c;

    while (!S.empty()) {
        u = S.top();
        S.pop();
        for (i = 0; i < G[u].size(); i++) {
            v = G[u][i];
            if (color[v] == -1) {
                color[v] = c;
                S.push(v);
            }
        }
    }

}

void assignColor () {

    int id = 1, i, u;

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

}

C++: #include<iostream>
#include<stdio.h>
#include<vector>
#include<queue>
#define MAX 100000
using namespace std;
int d[MAX];

int n;
vector <int> M[MAX];


int tail;



void BFS(int s,int t) {
	queue <int>Q;
	Q.push(s);
	d[s] = t;
	while (!Q.empty()) {
		s = Q.front();
		Q.pop();
		for (int j = 0; j < M[s].size(); j++) {
				
				if (d[M[s][j]] == -1) {
					d[M[s][j]] = t;
					Q.push(M[s][j]);
				}
		}

	}
}


int main() {
	int  m, s, t, q;
	scanf("%d %d", &n, &m);

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

	for (int i = 0; i < n; i++) {
		d[i] = -1;
	}
	int count = 0;
	for (int i = 0; i < n; i++) {
		if (d[i] == -1) {
			count++;
			BFS(i, count);
		}
	}
	cin >>q;
	for (int i = 0; i < q; i++) {
		int s2, t2;
		scanf("%d %d", &s2, &t2);
		if (d[s2] == d[t2]) {
			printf("yes\n");
		}
		else {
			printf("no\n");
		}
		
		
	}
	
	return 0;
}

C++: #include<iostream>
#include<vector>
using namespace std;
void numbering(int v, int k, vector<vector<int>>const&graph, vector<int>&id) {
	
	id[v] = k;
	//v????????????????????????
	//id??????????????°?????????????????????
	//k????????????????????????
	for (auto to : graph[v]) {
		//for(int i=0;i<graph[v].size();++i)
		
		if (id[to] != -1) {
			continue;
		}
		numbering(to, k, graph, id);
	}
}
int main() {
	int n, m;
	cin >> n >> m;
	vector<vector<int>>graph(n);
	for (int i = 0;i < m;++i) {
		int u, v;
		cin >> u >> v;
		graph[u].push_back(v);
		graph[v].push_back(u);
	}
	vector<int>id(n, -1);
	for (int i = 0;i < n;i++) {
		if (id[i] == -1) {
			numbering(i, i, graph, id);
			//numbering(?????????????????????,?????????????????????,graph,id)
		}
	}
	int q;
	cin >> q;
	while (q--) {
		int u, v;
		cin >> u >> v;
		if (id[u] == id[v]) {
			cout <<"yes" << endl;
		}
		else {
			cout << "no" << endl;
		}
	}

}

C++: #include <stdio.h>

int m[100000] = {0};

void init() {
	int i;
	for ( i = 0; i < 100000; ++i) {
		m[i] = i;
	}
}

int find(int n) {
	if ( n == m[n]) {
		return n;
	}
	return m[n] = find(m[n]);
}

int friend (int x, int y) {
	if ( find(x) == find(y)) {
		return 1;
	} else {
		return 0;
	}
}

void unit (int x, int y) {
	x = find(x);
	y = find(y);
	
	if ( x == y ) {
		return ;
	}
	m[y] = x;
}

int main() {
	int n, s, t, u, v, i;
	init();
	scanf("%d", &n);
	scanf("%d", &s);
	
	for ( i = 0; i < s; ++i) {
		scanf("%d", &u);
		scanf("%d", &v);
		unit( u, v);
	}
	
	scanf("%d", &t);
	
	for ( i = 0; i < s; i++) {
		scanf("%d", &u);
		scanf("%d", &v);
		if ( friend( u, v) == 1) {
			printf("yes\n");
		} else {
			printf("no\n");
		}
	}
	return 0;
}

C++: #include <iostream>
#include <cstdio>
#define MAX 100000

using namespace std;

int main(){
  int a[MAX]={};
  int n,m; cin>>n>>m;
  int s,t;
  int group=1;
  for(int i=0;i<m;i++){
    cin>>s>>t;
    if(a[s]==0 && a[t]==0){
      a[s]=a[t]=group;
      group++;
    }else if(a[s]==0){
      a[s]=a[t];
    }else if(a[t]==0){
      a[t]=a[s];
    }else{
      int tmp=a[t];
      a[t]=a[s];
      for(int j=0;j<i;j++){
        if(a[j]==tmp) a[j]=a[s];
      }
    }
  }

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

}

C++: #include<iostream>
#include<bits/stdc++.h>
using namespace std;
const int MAX=1e5+9;
int idx[MAX]={0};
void init(){
	int i;
	for(i=0;i<MAX;i++)
		idx[i]=i;
}
int findroot(int i){
	while(i!=idx[i])
		i=idx[i];
	return i;
}
void munion(int u ,int v){
	u=findroot(u);
	v=findroot(v);
	if(u!=v)
		idx[v]=u;
}
int main(){
	int i ,j ,n ,m;
	cin>>n>>m;
	init();
	while(m--){
		int x ,y;
		cin>>x>>y;
		munion(x ,y);
	}
	int q;
	cin>>q;
	while(q--){
		int  u ,v;
		cin>>u>>v;
		u=findroot(u);
		v=findroot(v);
		if(u==v)
			cout<<"Yes"<<"\n";
		else
			cout<<"No"<<"\n";
	}
}

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;
    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;
        }
    }
}