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++: #include <cstdio>
#include <cctype>
#include <vector>
using namespace std;

#define si static inline
#define gcu getchar_unlocked
si int in() {
	int c, n = 0;
	bool minus = false;
	if ((c = gcu()) == '-') minus = true; else ungetc(c, stdin);
	while ((c = gcu()) >= '0' && c <= '9') n = 10 * n + (c - '0');
	return minus ? -n : n; }
si void scan(char *s) {while (!isspace(*s++ = gcu()));}
#define pcu putchar_unlocked
#define svo si void out
template <typename T>
svo(T n) {
	static char buf[20];
	char *p = buf;
	if(n < 0) pcu('-'), n *= -1;
	if (!n) *p++ = '0';
	else while (n) *p++ = n % 10 + '0', n /= 10;
	while (p != buf) pcu(*--p); }
svo(const char *s){while(*s)pcu(*s++);}
svo(char *s){while(*s)pcu(*s++);}
svo(char c){pcu(c);}
template <typename T>
//svo(vector<T> &v){for(T &x:v)out(' '),out(x);out('\n');}
svo(vector<T> &v){for(T &x:v)out(&x == &v[0]?"":" "),out(x);out('\n');}
template <typename head, typename... tail>
svo(head&& h, tail&&... t){out(h);out(move(t)...);}

typedef vector<int> v;
struct graph {
	struct node {v n; int gid = 0;};
	vector<node> nodes;
	int gid_counter = 1;

	graph(int n) {
		nodes.resize(n);
	}
	void read(int n) {
		while (n--) {
			int s = in(), t = in();
			nodes[s].n.push_back(t);
			nodes[t].n.push_back(s);
		}
	}
	void traverse(int id, int gid) {
		node &n = nodes[id];
		if (n.gid)
			return;
		n.gid = gid ? gid : gid_counter++;
		for (int i: n.n)
			traverse(i, n.gid);
	}
	bool find(int s, int t) {
		traverse(s, nodes[s].gid);
		return nodes[s].gid == nodes[t].gid;
	}
};

int main() {
	int n = in(), m = in();
	graph g(n);
	g.read(m);
	int q = in();
	while (q--) {
		int s = in();
		out(g.find(s, in())? "yes" : "no", '\n');
	}
}

C++: #include<iostream>
#include<vector>
#include<stack>
#define MAX 100000
#define NIL -1

using namespace std;

int n;
vector<int> ver[MAX];
int grp[MAX];

void dfs(int r, int c);

int main() {
	int i, j, a, b, m, q, id = 1;
	
	cin >> n >> m;

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

	for (i = 0; i < n; i++)grp[i] = NIL;
	for (i = 0; i < n; i++) {
		if (grp[i] == NIL)dfs(i, id++);
	}

	cin >> q;

	for (i = 0; i < q; i++) {
		cin >> a >> b;
		if (grp[a] == grp[b])cout << "yes\n";
		else cout << "no\n";
	}
	return 0;
}

void dfs(int r, int c) {
	int i, u, v;
	stack<int> s;
	s.push(r);
	grp[r] = c;
	while (!s.empty()) {
		u = s.top();
		s.pop();
		for (i = 0; i < ver[u].size(); i++) {
			v = ver[u][i];
			if (grp[v] == NIL) {
				grp[v] = c;
				s.push(v);
			}
		}
	}
}

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

vector<vector<int> >g;
int n,m,q,s,t;

vector<bool>visited;
vector<int>color;
void dfs(int s){
    for(int i=0;i<g[s].size();i++){
        if(color[g[s][i]]==-1){
            color[g[s][i]]=color[s];
            dfs(g[s][i]);
        }
    }
}
bool dfs2(int s,int t){
    if(s==t)return true;
    visited[s]=true;
    for(int i=0;i<g[s].size();i++){
        if(!visited[g[s][i]]){
            if(dfs2(g[s][i],t)){
                return true;
            }
        }
    }
    return false;
}
int main() {
    scanf("%d %d",&n,&m);
    g.resize(n);
    color.resize(n,-1);
    for(int i=0;i<m;i++){
        scanf("%d %d",&s,&t);
        g[s].push_back(t);
        g[t].push_back(s);
    }
    for(int i=0;i<n;i++){
        if(color[i]==-1){
            color[i]=i;
            dfs(i);
        }
    }
    scanf("%d",&q);
    for(int i=0;i<q;i++){
        scanf("%d %d",&s,&t);
        for(int j=0;j<n;j++)visited[i]=false;
        string s1=(dfs2(s,t)?"yes":"no");
        string s2=(color[s]==color[t]?"yes":"no");
        if(s1!=s2&&s1=="yes")return 1;
        cout<<s2<<endl;
    }
    return 0;
}

C++: #include<cstdio>
#include<queue>
#include<vector>
#define N_MAX 100005
using namespace std;
struct Node{
    vector<int> vct;
    char type;
    char state;//0:undiscovered
};
vector<Node> nodes;
int n;
void bfs(){
    queue<int> Q;
    char type=1;
    for(int i=0;i<n;i++){
        if(nodes[i].state==0){
            Q.push(i);
            nodes[i].type = type;
            nodes[i].state = 1;
            while(!Q.empty()){
                int active = Q.front();
                int total = nodes[active].vct.size();
                for(int i=0;i<total;i++){
                    int newIndex=nodes[active].vct[i];
                    if(nodes[newIndex].state==0){
                        Q.push(newIndex);
                        //printf("== %d -> %d ==\n", active, newIndex);
                        nodes[newIndex].type = type;
                        nodes[newIndex].state = 1;
                    }
                }
                Q.pop();
            }
            type++;
        }
    }
}
int main(){
    int rel;
    scanf("%d%d", &n, &rel);
    for(int i=0;i<n;i++){//initial
        Node init;
        init.type=0;
        init.state=0;
        nodes.push_back(init);
        //printf("initial info: %d %d\n", init.type, init.state);
    }
    for(int i=0;i<rel;i++){
        int maj, sub;
        scanf("%d%d", &maj, &sub);
        nodes[maj].vct.push_back(sub);
        nodes[sub].vct.push_back(maj);//Undirected
    }
    bfs();
    short ques;
    scanf("%d", &ques);
    for(short i=0;i<ques;i++){
        int maj, sub;
        scanf("%d%d", &maj, &sub);
        if(nodes[maj].type==nodes[sub].type){
            printf("yes\n");
        }else{
            printf("no\n");
        }
    }

    /*printf("\n============ now testing ================\n");
    for(int i=0;i<n;i++){
        printf("\t-- %d: type:%d state:%d --\n", i, nodes[i].type, nodes[i].state);
    }*/
    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;
    int i, u, v;
    while ( !S.empty() ) {
        u = S.top();
        S.pop();
        for ( i = 0; i < G[u].size(); i++ ) {
            v = G[u][i];
            if ( color[v] == NIL ) {
                color[v] = c;
                S.push(v);
            }
        }
    }
}
  
void assignColor() {
    int id = 0;
    int i, u;
    for ( i = 0; i < n; i++ ) color[i] = NIL;
    for ( u = 0; u < n; u++ ) {
        if ( color[u] == NIL ) 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;
}