Go: package main

import (
	"bufio"
	"container/list"
	"fmt"
	"os"
	"strconv"
)

//util
var sc = bufio.NewScanner(os.Stdin)

func nextStr() string {
	sc.Scan()
	return sc.Text()
}

func nextInt() int {
	sc.Scan()
	i, e := strconv.Atoi(sc.Text())
	if e != nil {
		panic(e)
	}
	return i
}

func printList(list []int) {
	n := len(list)
	buf := bufio.NewWriter(os.Stdout)
	for _, v := range list[0 : n-1] {
		buf.Write([]byte(fmt.Sprintf("%d ", v)))
	}
	buf.Write([]byte(fmt.Sprintf("%d\n", list[n-1])))
	buf.Flush()
}

func max(a, b int) int {
	if a > b {
		return a
	} else {
		return b
	}
}

func min(a, b int) int {
	if a > b {
		return b
	} else {
		return a
	}
}

//solve
const (
	MAX = 100000
	NIL = -1
)

var (
	n, m, q, s, t int
	G             [MAX][]int //連結リスト
	color         [MAX]int
)

func dfs(r int, c int) {
	S := list.New()
	S.PushFront(r)
	color[r] = c
	for S.Len() != 0 {
		u := S.Remove(S.Front()).(int)
		for i := 0; i < len(G[u]); i++ {
			v := G[u][i]
			if color[v] == NIL {
				color[v] = c
				S.PushFront(v)
			}
		}
	}
}

//幅優先探索で、頂点を色付け
func assignColor() {
	id := 1
	for i := 0; i < n; i++ {
		color[i] = NIL
	}
	for i := 0; i < n; i++ {
		if color[i] == NIL {
			id++
			dfs(i, id)
		}
	}
}

func main() {
	sc.Split(bufio.ScanWords)
	n, m = nextInt(), nextInt()
	for i := 0; i < m; i++ {
		s, t = nextInt(), nextInt()
		if i == 0 {
			G[s] = make([]int, 0)
			G[t] = make([]int, 0)
		}
		G[s] = append(G[s], t)
		G[t] = append(G[t], s)

	}
	assignColor()
	q = nextInt()
	for i := 0; i < q; i++ {
		s, t = nextInt(), nextInt()
		if color[s] == color[t] {
			fmt.Println("yes")
		} else {
			fmt.Println("no")
		}
	}

}

C++: #include <cmath>
#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <climits>
#include <map>
#include <list>
#include <stack>
#include <queue>
#include <vector>
#include <string>
#include <sstream>
#include <fstream>
#include <iostream>
#include <algorithm>
using namespace std;
 
struct node {
    int id;
    vector<int> rel;
};

struct memo {
	int a, b;
	bool val;
	bool operator==(memo m){
		return (this->a == m.a && this->b == m.b) || (this->a == m.b && this->b == m.a);
	}
};
 
int n, m, q;
node* nodes;
vector<memo> ms;

bool canReach(int s, int d, bool* h){
    h[s] = true;
	if(s==d) return true;
	
	memo nm;
	nm.a = s;
	nm.b = d;
	
	vector<memo>::iterator it = find(ms.begin(), ms.end(), nm);
	if(it != ms.end()) return (*it).val;
	
    for(int i = 0; i < nodes[s].rel.size(); i++){
		if(!h[nodes[s].rel[i]] && canReach(nodes[s].rel[i], d, h)){
			nm.val = true;
			ms.push_back(nm);
			return true;
        }
    }
	
	nm.val = false;
	ms.push_back(nm);
    return false;
}
 
int main() {
    scanf("%d %d", &n, &m);
     
    nodes = new node[n];
    for(int i = 0; i < n; i++){
        nodes[i].id = i;
    }
    while(m--){
        int l, r;
        scanf("%d %d", &l, &r);
        nodes[l].rel.push_back(r);
        nodes[r].rel.push_back(l);
    }
     
    scanf("%d", &q);
    while(q--){
        int l, r;
        scanf("%d %d", &l, &r);
         
        bool *h = new bool[n];
        for(int i = 0; i < n; i++){
            h[i] = false;
        }
        printf("%s\n", canReach(l, r, h) ? "yes" : "no");
        delete[] h;
    }
    return 0;
}

C++: def dfs(s):
    global t
    if s == t:
        return True
    DP[s]=1
    for i in F[s]:
        if not DP[i]:
            if dfs(i):
                return True
    return False
    
n,m = [int(i) for i in input().split()]
F = [{}]*n
for _ in range(m):
    i,j = [int(i) for i in input().split()]
    F[i][j] = 1
    F[j][i] = 1
q = int(input())
for i in range(q):
    DP = [0]*n
    s,t = [int(i) for i in input().split()]
    if dfs(s):
        print("yes")
    else:
        print("no")

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

struct node {
    int to;
    node *next;
};

node *adj[100000], fm[200000];
int g[100000];

int main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);
    int n, m, i;
    cin>>n>>m;
    m+=m;
    int s, t;
    i=0;
    while(i<m) {
        cin>>s>>t;
        fm[i].to=t;
        fm[i].next=adj[s];
        adj[s]=&fm[i];
        i++;
        fm[i].to=s;
        fm[i].next=adj[t];
        adj[t]=&fm[i];
        i++;
    }
    int group=1;
    vector<int> st;
    st.reserve(n);
    for(i=0; i<n; i++) {
        if(g[i]) continue;
        g[i]=group;
        st.push_back(i);
        while(!st.empty()) {
            node *p=adj[st.back()];
            g[st.back()]=group;
            st.pop_back();
            while(p) {
                if(g[p->to]==0) st.push_back(p->to);
                p=p->next;
            }
        }
        group++;
    }
    cin>>n;
    for(int i=0; i<n; i++) {
        cin>>s>>t;
        if(g[s]==g[t]) cout<<"yes\n";
        else cout<<"no\n";
    }
    return 0;
}

C++: #define _USE_MATH_DEFINES

#include <cstdio>
#include <cstdlib>
#include <iostream>
#include <cmath>
#include <algorithm>
#include <vector>
#include <queue>
#include <map>
#include <list>

long long int INF = 1e18;
using namespace std;

typedef pair<long long int, long long int> P;

#define MAX_N 200000

int par[MAX_N];
int rnk[MAX_N];

// 初期化
void init(int n){
	for(int i = 0; i < n; i++){
		par[i] = i;
		rnk[i] = 0;
	}
}

// x の親を返す
int find(int x){
	if(par[x] == x){
		return x;
	}
	return par[x] = find(par[x]);
}

// x と y を併合する
void unite(int x, int y){
	int x_par = find(x);
	int y_par = find(y);
	if(x_par == y_par){
		return;
	}
	
	if(rnk[x_par] < rnk[y_par]){
		par[x_par] = y_par;
	}else{
		par[y_par] = x_par;
		if(rnk[x_par] == rnk[y_par]){
			rnk[x_par]++;
		}
	}
}

// x, y が同じグループか判定
bool same(int x, int y){
	return (find(x) == find(y));
}

int main(){
	
	int n, m;
	cin >> n >> m;
	
	init(n);
	
	for(int i = 0; i < m; i++){
		int x, y;
		cin >> x >> y;
		unite(x, y);
	}
	
	int q;
	cin >> q;
	
	for(int i = 0; i < q; i++){
		int x, y;
		cin >> x >> y;
		if(same(x, y)){
			cout << "yes" << endl;
		}else{
			cout << "no" << endl;
		}
	}
	
	return 0;
}

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

using namespace std;
using Relations = vector<vector<int>>;

const int no_group = -1;
const int no_user_id = -1;

void depth_first_search(Relations& list_graph, int started_user_id, vector<int>& connected_group, int group_id) {
  stack<int> visited_path;
  visited_path.push(started_user_id);
  connected_group[started_user_id] = group_id;

  while(!visited_path.empty()) {
    int current_user_id = visited_path.top();

    int unvisited_adjacency_user_id = no_user_id;
    for(int i = 0; i < list_graph[current_user_id].size(); i++) {
      int adjacency_user_id = list_graph[current_user_id][i];
      if(connected_group[adjacency_user_id] == no_group) {
        unvisited_adjacency_user_id = adjacency_user_id;
        break;
      }
    }

    if(unvisited_adjacency_user_id != no_user_id) {
      connected_group[unvisited_adjacency_user_id] = group_id;
      visited_path.push(unvisited_adjacency_user_id);
    } else {
      visited_path.pop();
    }
  }
}


int main() {
  int user_num;
  int relation_num;
  Relations list_graph;

  // Init
  cin >> user_num >> relation_num;
  list_graph.resize(user_num);

  // Construct list graph
  for(int i = 0; i < relation_num; i++) {
    int user1_id, user2_id;
    cin >> user1_id >> user2_id;
    list_graph[user1_id].push_back(user2_id);
    list_graph[user2_id].push_back(user1_id);
  }

  // Group connected component
  vector<int> connected_group(user_num, no_group);

  int group_id = 0;
  for(int i =  0; i < user_num; i++) {
    if(connected_group[i] == no_group) {
      depth_first_search(list_graph, i, connected_group, group_id++);
    }
  }


  // Answer queries
  int query_num;
  cin >> query_num;
  for(int i = 0; i < query_num; i++) {
    int user1_id, user2_id;
    cin >> user1_id >> user2_id;

    if(connected_group[user1_id] == connected_group[user2_id]) {
      cout << "yes";
    } else {
      cout << "no";
    }
    cout << endl;
  }
}