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<vector>
using namespace std;
int cnt=1;
struct Point{
	int x;
	int y;
};

bool depth(vector< vector<int> > &vv,vector<int> &f,int num1,int num2){
	
	f[num1]=cnt;
	cnt++;
	
	for(int i=0; i<vv[num1].size(); i++){
		if(vv[num1][i]!=0 && f[i]==0){
			depth(vv,f,i,num2);
		}
	}

	if(f[num2]!=0){
		return 1;
	}else{
		return 0;
	}	

}
int main(){
	int n,m,l;
	cin>>n>>m;
	vector< vector<int> > v(n,vector<int> (n,0));
	for(int i=0; i<m; i++){
		Point a;
		cin>>a.x>>a.y;
		v[a.x][a.y]=1;
	}
	cin>>l;
	vector<string> ans(l);
	for(int i=0; i<l; i++){
		Point b;
		cin>>b.x>>b.y;
		vector<int> ft(n,0);
		int tmp;
		if(b.y<b.x){
			tmp=b.y;
			b.y=b.x;
			b.x=tmp;
		}
		if(depth(v,ft,b.x,b.y)){
			ans[i]="yes";
		}else{
			ans[i]="no";
		}
	}
	for(int i=0; i<l; i++){
		cout<<ans[i]<<endl;
	}
  return 0;
}

C++: #include<iostream>
#include<string>
#include<cstdio>
#include<algorithm>
#include<queue>
using namespace std;


int n;

string *color;

queue<int> q;

int *ans;

vector<int> g[1000000];


void bfs(int x){
  color[x] = "gray";
  q.push(x);


  while(q.size() != 0){
    int u = q.front();
    q.pop();

    for(int i = 0; i < g[u].size(); i++){
      int v = g[u][i];
      if(color[v] == "white"){
        color[v] = "gray";
        q.push(v);
      }
    }

    color[u] = "black";
    ans[u] = x;


  }
  return;
}


int main(){

  cin >> n;

  color = new string[n];

  ans = new int[n];

  int m;

  cin >> m;


  int a, b;


  for(int i = 0; i < m; i++){
    cin >> a >> b;
    g[a].push_back(b);
    g[b].push_back(a);
  }


  for(int i = 0; i < n; i++){
    color[i] = "white";
  }


  for(int j = 0; j < n; j++){
    if(color[j] == "white"){
      bfs(j);
    }
  }

  int q;

  cin >> q;

  for(int i = 0; i < q; i++){
    cin >> a >> b;
    if(ans[a] == ans[b]){
      cout << "yes" << endl;
    }
    else{
      cout << "no" << endl;
    }
  }

  return 0;
}

C++: #include <cassert>
#include <cstdio>
#include <algorithm>
#include <iostream>
#include <vector>
#include <list>

class TVertex
{
    int FIndex;
    int FCommuniyId;
    std::list<TVertex*> FList;

public:
    TVertex(int Index)
     : FIndex(Index), FCommuniyId(0)
    {}
    void AddPath(TVertex* Vertex)
    {
        FList.push_back(Vertex);
    }
    void SetCommunity(int CommunityId)
    {
        if(FCommuniyId) return;
        FCommuniyId = CommunityId;
        for(std::list<TVertex*>::iterator It = FList.begin(); It != FList.end(); ++It){
            TVertex* V = *It;
            V->SetCommunity(CommunityId);
        }
    }
    int CommunityId()const
    {
        return FCommuniyId;
    }
};
class TGraph
{
    std::vector<TVertex*> FTable;
    void Init(int n)
    {
        assert(n > 0);
        FTable.resize(n);
        for(int i = 0; i < n; ++i){
            FTable[i] = new TVertex(i);
        }
    }
public:
    TGraph(int n)
    {
        Init(n);
    }
    void MakeFriend(int s, int t)
    {
        assert(s < FTable.size());
        assert(t < FTable.size());
        FTable[s]->AddPath(FTable[t]);
        FTable[t]->AddPath(FTable[s]);
    }
    void SetCommunity()
    {
        for(std::size_t i = 0; i < FTable.size(); ++i){
            FTable[i]->SetCommunity(i+1);
        }
    }
    bool IsSameCommunity(int s, int t)const
    {
        assert(s < FTable.size());
        assert(t < FTable.size());
        return FTable[s]->CommunityId() == FTable[t]->CommunityId();
    }
};

int main()
{
    int n, m;
    std::scanf("%d %d", &n, &m);
    TGraph Graph(n);
    for(int i = 0; i < m; ++i){
        int s, t;
        std::scanf("%d %d", &s, &t);
        Graph.MakeFriend(s, t);
    }
    int q;
    std::scanf("%d", &q);
    Graph.SetCommunity();
    for(int i = 0; i < q; ++i){
        int s, t;
        std::scanf("%d %d", &s, &t);
        std::printf("%s\n", (Graph.IsSameCommunity(s, t) ? "yes" : "no"));
    }
    return 0;
    
}

C++: #include <iostream>
#include <algorithm>
#include <vector>
#include<string>
#include <set>
#include <map>
#include <queue>
#include <limits.h>
#include <cmath>

using namespace std;

#define rip(i,n,s) for (int i=(s);i<(int)(n);i++)
#define all(a) (a).begin(),(a).end()
typedef long long ll;

struct UnionFind{
    int size;
    vector<int> par;
    vector<int> rank;
    UnionFind(int x){
        size=x;
        par=vector<int> (x);
        rank=vector<int> (x,1);
        for (int i=0;i<x;i++){
            par[i]=i;
        }
    }
    int root(int x){
        if(par[x]==x){
            return x;
        }
        else{
            return par[x]=root(par[x]);
        }
    }
    void unite(int x,int y){
        x=root(x);y=root(y);
        if(x==y){
            return;
        }
        if(rank[x]<rank[y]){
            par[x]=y;
        }
        else{
            par[y]=x;
        }
        if(rank[x]==rank[y]){
            rank[x]++;
        }
    }
    bool check(int x,int y){
        return root(x)==root(y);
    }
    void initialize(){
        for (int i=0;i<size;i++){
            par[i]=i;
        }
    }
};

int main(){
    int n,m;
    cin >> n >> m;
    UnionFind uf(n);
    int a,b;
    rip(i,m,0){
        cin >> a >> b;
        uf.unite(a,b);
    }
    int q;
    cin >> q;
    vector<bool> ans(q);
    rip(i,q,0){
        cin >> a >> b;
        ans[i]=uf.check(a,b);
    }
    rip(i,q,0){
        if(ans[i]){
            printf("yes\n");
        }
        else{
            printf("no\n");
        }
    }
}

C++: #include<iostream>
#include<vector>
#include<stack>
using namespace std;
static const int MAX = 100000;
static const int NIL = -1;

int n, color[MAX];
vector<int> G[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;
		}
	}	
	
	return 0;	
}