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<bits/stdc++.h>
using namespace std;

int n,m,q;
int s,t;
int ck[100002];
list<int>l[100002];
list<int>ans[100002];
queue<int>que;

int slv(int x);

int main(){
  cin>>n>>m;
  for(int i=0;i<n;i++)ck[i]=0;
  for(int i=0;i<m;i++){
    cin>>s>>t;
    l[s].push_back(t);
    l[t].push_back(s);
  }

  for(int i=0;i<n;i++){
    if(ck[i]==0){
      while(!que.empty())que.pop();
      que.push(i);
      slv(i);
    }
  }

  cin>>q;
  for(int i=0;i<q;i++){
    cin>>s>>t;
    int flag=0;
    for(int j=0;j<ans[s].size();j++){
      int x=ans[s].front();
      ans[s].pop_front();
      ans[s].push_back(x);
      if(x==t){
	flag=1;
	break;
      }
    }
    if(flag==1)cout<<"yes"<<endl;
    else cout<<"no"<<endl;
  }

}

int slv(int x){
  for(int i=0;i<l[x].size();i++){
    int y=l[x].front();
    l[x].pop_front();
    l[x].push_back(y);

    for(int j=0;j<que.size();j++){
      int z=que.front();
      que.pop();
      que.push(z);
      ans[z].push_back(y);
      ans[y].push_back(z);
    }

    if(ck[y]==0){
      que.push(y);
      ck[y]=1;
      slv(y);
    }
  }
  return(0);
}

C++: #include <iostream>
#include <vector>

using namespace std;

class UnionFindTree {
private:
    vector<int32_t> parent, rank;

    int32_t find(int32_t x) {
        if (parent[x] == x) {
            return x;
        } else {
            int32_t p = find(parent[x]);
            parent[x] = p;
            return p;
        }
    }

public:
    UnionFindTree(int32_t n) {
        parent.resize(n);
        rank.resize(n);

        for (int32_t i = 0; i < n; i++) {
            parent[i] = i;
            rank[i] = 0;
        }
    }

    void unite(int32_t x, int32_t y) {
        x = find(x);
        y = find(y);

        if (x == y) return;

        if (rank[x] < rank[y]) {
            parent[x] = y;
        } else {
            parent[y] = x;
            if (rank[x] == rank[y]) rank[x]++;
        }
    }

    bool same(int32_t x, int32_t y) {
        return find(x) == find(y);
    }
};

int main() {
    int32_t n, m;
    cin >> n >> m;

    UnionFindTree uf(n);

    for (int32_t i = 0; i < m; i++) {
        int32_t s, t;
        cin >> s >> t;

        uf.unite(s, t);
    }

    int32_t q;
    cin >> q;

    for (int32_t i = 0; i < q; i++) {
        int32_t s, t;
        cin >> s >> t;

        cout << (uf.same(s, t) ? "yes" : "no") << endl;
    }

    return 0;
}

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

int n, m, s, t, u;
vector<vector <int> > a;
bool f[100000];

bool path(int s1) {
	f[s1] = 1;
	for (int i = 0; i < (int) a[s1].size(); i++) {
		if (a[s1][i] == t) {
			return true;
		}
		else if (!f[a[s1][i]])
			if (path(a[s1][i]))
				return true;
	}
	return false;
}

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

	a.resize(n);

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

	int q;
	cin >> q;
	for (int i = 0; i < q; i++) {
		cin >> s >> t;

	for (int i = 0; i < n; i++)
		f[i] = 0;

		if(path(s))
			cout << "yes" << endl;
		else
			cout << "no" << endl;
	}

	return 0;
}

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;
    }
  }

  return 0;
}

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

typedef struct box { int val; box *prev, *next; } box_t;

box_t* init()
{
    box_t* head = new box_t;
    head->val = -1;
    head->next = NULL;
    head->prev = NULL;
    return head;
}

box_t* make_tail(box_t* head)
{
    box_t* tail = new box_t;
    tail->val = -1;
    head->next = tail;
    tail->next = NULL;
    tail->prev = head;
    return tail;
}

bool isEmpty(box_t* head, box_t* tail)
{
    return (head->next == tail ? true : false);
}

box_t* f_insert(box_t* head, int data)
{
    box_t* box = new box_t;
    box->val = data;
    box->next = head->next;
    box->prev = head;
    head->next->prev = box;
    head->next = box;
    return box;
}

int b_pop(box_t* tail)
{
    if(!(tail->prev->prev)) return -1;
    box_t* box = tail->prev;
    int val;
    val = tail->prev->val;
    tail->prev = box->prev;
    box->prev->next = tail;
    delete box;
    return val;
}

void clear(box_t* head, box_t* tail)
{
    box_t* box1 = head->next;
    box_t* box2;
    if(box1 == tail) return;
    while(box1 != tail){
        box2 = box1->next;
        delete box1;
        box1 = box2;
    };
    head->next = tail;
    tail->prev = head;
    return;
}

int main()
{
    int G[5000][70];
    int *dist;

    box_t* head = init();
    box_t* tail = make_tail(head);

    int n, i, j, e, q, v1, v2;
    scanf("%d", &n);

	dist = new int [n];

    for(i = 0; i < n; i++){
        for(j = 0; j < n; j++){ G[i][j] = 0; } }
    int m;
    scanf("%d", &m);
    for(int k = 0; k < m; k++){
        scanf("%d %d", &i, &j);
        G[i][0]++; G[j][0]++;
        G[i][G[i][0]] = j;
        G[j][G[j][0]] = i;
    }
    scanf("%d", &q);
    int self, friends;
    bool is_connected;

    for(int k = 0; k < q; k++){
        for(j = 0; j < n; j++) dist[j] = -1;

        scanf("%d %d", &self, &friends);
        f_insert(head, self);
        dist[self] = 0;
        is_connected = false;

        while(1){
            v1 = b_pop(tail);
            e = G[v1][0];
            for(i = 1; i <= e; i++){
                v2 = G[v1][i];
                if(dist[v2] < 0){
                    dist[v2] = dist[v1] + 1;
                    f_insert(head, v2);
                }
            }
            if(dist[friends] > 0){
                is_connected = true;
                break;
            }
            if(isEmpty(head, tail)) break;
        };
        if(is_connected){ printf("yes\n"); }else{ printf("no\n"); }
        if(!isEmpty(head, tail)) clear(head, tail);
    }

	delete [] dist;

    return 0;
}