Go: package main

import (
	"fmt"
	"bufio"
	"os"
	"strconv"
)

func main() {
	var n,m int
	fmt.Scan(&n)
	group := make([]int, n)
	for i := 0; i < n; i++ {
		group[i] = i
	}
	
	fmt.Scan(&m)
	sc := bufio.NewScanner(os.Stdin)
	sc.Split(bufio.ScanWords)
	for i := 0; i < m; i++ {
		sc.Scan()
		s, _ := strconv.Atoi(sc.Text())
		sc.Scan()
		t, _ := strconv.Atoi(sc.Text())

		if group[s] < group[t] {
			group[t] = group[s]
		} else {
			group[s] = group[t]
		}
	}

	sc.Scan()
	q, _ := strconv.Atoi(sc.Text())
	for i := 0; i < q; i++ {
		sc.Scan()
		s, _ := strconv.Atoi(sc.Text())
		sc.Scan()
		t, _ := strconv.Atoi(sc.Text())

		if root(s, &group) == root(t, &group) {
			fmt.Println("yes")
		} else {
			fmt.Println("no")
		}
	}
}

func root(i int, group *[]int) int {
	if i == (*group)[i] {
		return i
	}
	(*group)[i] = root((*group)[i], group)
	return (*group)[i]
}

C++: /*
** Connected Components
*/

# include <cstdio>
# include <cstring>
# include <vector>
# include <queue>
using namespace std;

const int MAX = 100000;

int n, m, q, c[MAX];
vector<int> g[MAX];

void init() {
    scanf("%d%d", &n, &m);
    int u, v;
    while (m--) {
        scanf("%d%d", &u, &v);
        g[u].push_back(v);
        g[v].push_back(u);
    }
}

bool find_con(int u, int v) {
    queue<int> que;
    que.push(u);
    memset(c, 0, sizeof(c));
    c[u] = 1;
    bool rec = false;

    while (!que.empty()) {
        int t = que.front();
        que.pop();
        for (int i = 0; i < g[t].size(); i++) {
            if (g[t][i] == v) {
                return true;
            }
            if (c[g[t][i]] == 0) {
                c[g[t][i]] = 1;
                que.push(g[t][i]);
            }
        }
    }

    return rec;
}

void solve() {
    init();
    scanf("%d", &q);
    int u, v;
    while (q--) {
        scanf("%d%d", &u, &v);
        if (find_con(u, v)) {
            printf("yes\n");
        }
        else
        {
            printf("no\n");
        }
    }
}

int main() {
    // freopen("infile", "r", stdin);
    // freopen("outfile", "w", stdout);
    solve();
    return 0;
}

C++: #include<stdio.h>
#include<queue>

#define MAX 10000

int G[MAX+1][MAX+1];
int n, m;

bool bfs(int src, int dest) {
    bool C[MAX];
    for (int i = 0; i < n; ++i) C[i] = false;

    std::queue<int> Q;
    Q.push(src);
    while(!Q.empty()) {
        int cur = Q.front();Q.pop();
        for (int i = 0; i < n; ++i) {
            if (G[cur][i] == 0) continue;
            if (C[i]) continue;
            if (i == dest) return true;
            Q.push(i);
            C[i] = true;
            //printf("s:%d, cur:%d, i:%d\n", src, cur, i);
        }
    }

    return false;
}

int main() {
    scanf("%d %d", &n, &m);
    for (int i = 0; i < n; ++i) {
        for (int j = 0; j < n; ++j) {
            G[i][j] = 0;
        }
    }
    for (int i = 0; i < m; ++i) {
        int u,k;
        scanf("%d %d", &u, &k);
        G[u][k] = 1;
        G[k][u] = 1;
    }

    int q;
    scanf("%d", &q);
    for (int i = 1; i <= q; ++i) {
        int s,d;
        scanf("%d %d", &s, &d);
        bfs(s, d) ? printf("yes\n") : printf("no\n");
    }

    return 0;
}

C++: #include<stdio.h>
#include<queue>

using namespace std;

const int MAX = 100000;

int parent(int table[], int child) {
	queue<int> q;

	while (table[child] != -1) {
		q.push(child);
		child = table[child];
	}
	while (!q.empty()) {
		table[q.front()] = child;
		q.pop();
	}
	return child;
}

int main() {
	int n, m, q;
	int table[MAX];

	scanf("%d %d", &n, &m);

	for (int i = 0; i < n; i++)table[i] = -1;
	for (int i = 0; i < m; i++) {
		int s, t;
		scanf("%d %d", &n, &m);
		
		int ps = parent(table, s);
		int pt = parent(table, t);
		if (ps != pt) {
			table[ps] = pt;
		}
	}

	scanf("%d", &q);

	for (int i = 0; i < q; i++) {
		int s, t;
		
		scanf("%d %d", &n, &m);

		int ps = parent(table, s);
		int pt = parent(table, t);

		if (ps == pt) {
			printf("yes\n");
		}
		else {
			printf("no\n");
		}
	}
	return 0;
}

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

using namespace std;

int main() {
  vector<int> R[100000];
  queue<int> Q;
  int n,m,s,t,q;
  int visit[100000];

  cin >> n >> m;
  for(int i=0;i<m;i++){
    cin >> s >> t;
    R[s].push_back(t);
    R[t].push_back(s);
  }
  cin >> q;
  for(int i=0;i<q;i++){
    cin >> s >> t;
    for(int j=0;j<n;j++) visit[j] = 0;
    Q.push(s);
    int f=0;
    while(Q.empty() == false && f==0){
      int u = Q.front();
      Q.pop();
      visit[u] = 1;
      if(u==t){
	f = 1;
	break;
      }
      for(int j=0;j<R[u].size();j++){
	int v = R[u][j];
	if(visit[v]==0) Q.push(v);
      }
    }
    if(f==1) cout << "yes" << endl;
    else cout << "no" << endl;
  }

  return 0;
}

C++: #include <cstdio>
#include <cstdlib>
#include <queue>
using namespace std;

int n;
bool **connection;

bool isFriend(int s, int t){
    int i;
    bool f[n];
    for(i=0;i<n;i++)f[i]=false;
    f[s]=true;
    int u;
    queue<int> q;
    q.push(s);
    while(!q.empty()){
        u=q.front();q.pop();
        for(i=0;i<n;i++){
            if(connection[u][i]&&f[i]==false){
                connection[u][i]=true;
                connection[i][u]=true;
                if(i==t)return true;
                f[i]=true;
                q.push(i);
            }
        }
    }
    return false;
}

int main(){
    int i, j, m, s, t, q;
    scanf("%d %d",&n,&m);
    connection = (bool **)malloc(sizeof(bool *)*n);
    for(i=0;i<n;i++){
        connection[i] = (bool *)malloc(sizeof(bool)*n);
        for(j=0;j<n;j++){
            connection[i][j]=0;
        }
    }
    for(i=0;i<m;i++){
        scanf("%d %d",&s,&t);
        connection[s][t]=true;
        connection[t][s]=true;
    }
    scanf("%d",&q);
    for(i=0;i<q;i++){
        scanf("%d %d",&s,&t);
        if(isFriend(s,t))printf("yes\n");
        else printf("no\n");
    }
    return 0;
}

C++: #define _USE_MATH_DEFINES
#include "bits/stdc++.h"
using namespace std;

//#define int long long
#define DBG 1
#define dump(o) if(DBG){cerr<<#o<<" "<<o<<endl;}
#define dumpc(o) if(DBG){cerr<<#o; for(auto &e:(o))cerr<<" "<<e;cerr<<endl;}
#define rep(i,a,b) for(int i=(a);i<(b);i++)
#define rrep(i,a,b) for(int i=(b)-1;i>=(a);i--)
#define each(it,c) for(auto it=(c).begin();it!=(c).end();it++)
#define all(c) c.begin(),c.end()
const int INF = sizeof(int) == sizeof(long long) ? 0x3f3f3f3f3f3f3f3fLL : 0x3f3f3f3f;
const int MOD = (int)(1e9 + 7);
vector<vector<int>>vec;
int n;
vector<int>color;
void bsf(int s,int c) {
	queue<int>q;
	q.push(s);
	color[s] = c;
	while (!q.empty()) {
		int u = q.front(); q.pop();
		rep(v, 0, vec[u].size()) {
			if (color[vec[u][v]] != -1)continue;
			color[vec[u][v]] = c;
			q.push(vec[u][v]);
		}
	}
}
void solve() {
	rep(i, 0, n) {
		if (color[i] == -1)bsf(i, i);
	}
}
signed main() {
	cin >> n; vec = vector<vector<int>>(n); color = vector<int>(n, -1);
	int m; cin >> m;
	rep(i, 0, m) {
		int s, t; cin >> s >> t;
		vec[s].push_back(t);
		vec[t].push_back(s);
	}
	solve();
	int q; cin >> q;
	rep(i, 0, q) {
		int s, t; cin >> s >> t;
		if (color[s] == color[t])cout << "YES" << endl;
		else cout << "NO" << endl;
	}
	return 0;
}