Go: package main

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

var scanner = bufio.NewScanner(os.Stdin)

func nextString() string {
	scanner.Scan()
	return scanner.Text()
}

func nextInt() int {
	n, err := strconv.Atoi(nextString())
	if err != nil {
		fmt.Printf("strconv.Atoi failed: %v\n", err)
	}
	return n
}

func newGraph(nNodes int) *Graph {
	g := Graph{}
	g.nodes = make([]*GraphNode, nNodes)
	for iNode := 0; iNode < len(g.nodes); iNode++ {
		g.nodes[iNode] = &GraphNode{}
		g.nodes[iNode].key = GraphNodeKey(iNode)
	}
	return &g
}

var infty = 1000000000

type GraphNodeKey int

// GraphNode is a node for undirected graph
type GraphNode struct {
	key       GraphNodeKey
	adjacents []*GraphNode
	visited   bool
	d, f      int
	parent    *GraphNode
	cc        int
}

func (g *Graph) setAdjacent(l, r GraphNodeKey) {
	g.nodes[l].adjacents = append(g.nodes[l].adjacents, g.nodes[r])
}

// Graph is a undirected graph
type Graph struct {
	nodes []*GraphNode
}

func (g *Graph) initialize() {
	for iNode := 0; iNode < len(g.nodes); iNode++ {
		g.nodes[iNode].visited = false
		g.nodes[iNode].d = infty
		g.nodes[iNode].f = infty
		g.nodes[iNode].parent = nil
		g.nodes[iNode].cc = -1 // 22.3-12
	}
}

type QueueEntry struct {
	node *GraphNode
	next *QueueEntry
}

type Queue struct {
	head, tail *QueueEntry
}

func (q *Queue) enqueue(node *GraphNode) {
	entry := QueueEntry{}
	entry.node = node

	if q.tail == nil {
		q.head = &entry
		q.tail = &entry
		return
	}

	q.tail.next = &entry
	q.tail = q.tail.next
}

func (q *Queue) dequeue() *QueueEntry {
	if q.head == nil {
		return nil
	}
	poped := q.head
	q.head = q.head.next
	if q.head == nil {
		q.tail = nil
	}
	return poped
}

func (q *Queue) isEmpty() bool {
	return q.head == nil
}

var time = 0

func fillDistancesByDepthFirstSearch(g *Graph) {
	g.initialize()
	time = 0
	cc := 0

	for _, u := range g.nodes {
		if !u.visited {
			dfsVisit(g, u, cc)
			cc++
		}
	}
}

func dfsVisit(g *Graph, u *GraphNode, cc int) {
	time++
	u.d = time
	u.cc = cc

	u.visited = true
	for _, v := range u.adjacents {
		if !v.visited {
			v.parent = u
			dfsVisit(g, v, cc)
		}
	}
	time++
	u.f = time
}

func main() {
	scanner.Split(bufio.ScanWords)

	nUsers := nextInt()
	nEdges := nextInt()
	graph := newGraph(nUsers)
	for iEdge := 0; iEdge < nEdges; iEdge++ {
		l := GraphNodeKey(nextInt())
		r := GraphNodeKey(nextInt())
		graph.setAdjacent(l, r)
		graph.setAdjacent(r, l)
	}

	fillDistancesByDepthFirstSearch(graph)

	nQueries := nextInt()
	for iQuery := 0; iQuery < nQueries; iQuery++ {
		l := GraphNodeKey(nextInt())
		r := GraphNodeKey(nextInt())

		// fmt.Println(graph.nodes[l].d, graph.nodes[r].d, graph.nodes[r].f, graph.nodes[l].f)
		if graph.nodes[l].cc == graph.nodes[r].cc {
			fmt.Println("yes")
		} else {
			fmt.Println("no")
		}
	}
}

C++: #include <bits/stdc++.h>
using namespace std;
#define REP(i, s, n) for (int i = s; i < n; ++i)
#define rep(i, n) REP(i, 0, n)
#define SORT(c) sort((c).begin(), (c).end())
#define IINF INT_MAX
#define LLINF LLONG_MAX
#define DEBUG true
// sort(a.begin(), a.end(), std::greater<int>());

/*
std::vector<std::string> split(const std::string &input, char delimiter)
{
    std::istringstream stream(input);

    std::string field;
    std::vector<std::string> result;
    while (std::getline(stream, field, delimiter))
    {
        result.push_back(field);
    }
    return result;
}
*/
pair<int, int> data[100000];
bool finds[100000];
int n, m;
/*
int dfs(int foo, int timer)
{
    //foo is node number
    if (finds[foo].first != -1)
        return timer;
    finds[foo].first = ++timer;
    int result = timer;
    if (data[foo].size() != 0)
    {
        rep(i, data[foo].size())
        {
            result = dfs(data[foo][i], result);
        }
    }
    finds[foo].second = ++result;
    return result;
}
*/

bool dfs(int foo, int goal)
{
    bool ans = false;
    rep(i, m)
    {
        if (data[i].first == foo && data[i].second == goal)
            return true;
        if (data[i].first == foo)
        {
            if (finds[i] == true)
                continue;
            finds[i] = true;
            ans = dfs(data[i].second, goal);
        }
    }
    return ans;
}
int main()
{
    cin >> n >> m;
    rep(i, m)
    {
        cin >> data[i].first >> data[i].second;
    }
    int q;
    cin >> q;
    rep(i, q)
    {
        int left, right;
        cin >> left >> right;
        if (dfs(left, right) || dfs(right, left))
            cout << "yes";
        else
            cout << "no";
        cout << endl;
        rep(j, m) finds[j] = false;
    }
    return 0;
}

C++: #include <bits/stdc++.h>
#include <stdint.h>

typedef uint32_t u32;

template<u32 N_>
class UnionFindTree {
private:
  u32 par[N_];
  u32 rank[N_];
public:
  UnionFindTree(u32 n) {
    assert(n < N_);
    for(u32 i = 0; i < n; ++i) {
      par[i] = i;
      rank[i] = 0;
    }
    return;
  }
  int find(u32 x) {
    if( par[x] == x ) return x;
    return par[x] = find(par[x]);
  }
  void unite(u32 x, u32 y) {
    x = find(x);
    y = find(y);
    if( x == y ) return;
    if( rank[x] < rank[y] ) {
      par[x] = y;
      return;
    }
    par[y] = x;
    if( rank[x] == rank[y] ) rank[x] += 1;
    return;
  }  
};

int main() {

  u32 n, m;
  std::cin >> n >> m;

  UnionFindTree<200000> uft(m);

  for(u32 i = 0; i < m; ++i) {
    u32 x, y;
    std::cin >> x >> y;
    uft.unite(x, y);
  }

  u32 q;
  std::cin >> q;

  for(u32 i = 0; i < q; ++i) {
    u32 x, y;
    std::cin >> x >> y;
    std::cout << (uft.find(x) == uft.find(y) ? "yes" : "no") << std::endl;
  }
  
  return 0;
}

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

void set_color(const vector<vector<int> >& u, int p, vector<int>& color, int c) {
    if (color[p] != -1) return;
    color[p] = c;
    for (int i = 0; i < u[p].size(); i++) {
        set_color(u, u[p][i], color, c);
    }
}

bool is_friend(const vector<vector<int> >& u, int s, int t){
    vector<int> color(u.size(), -1);
    int c = 0;
    set_color(u, s, color, c++);
    return color[s] == color[t];
}
int main(){
    int n, m;
    cin >> n >> m;
    vector<vector<int> > u(n);
    for (int i = 0; i < m; i++) {
        int s, t;
        cin >> s >> t;
        u[s].push_back(t);
        u[t].push_back(s);
    }
    int q;
    cin >> q;
    for (int i = 0; i < q; i++) {
        int s, t;
        cin >> s >> t;
        if (is_friend(u, s, t)) {
            cout << "yes" << endl;
        } else {
            cout << "no"  << endl;
        }
    }
    return 0;
}

C++: #include<iostream>
#include<climits>
#include<vector>
#include<list>
#include<functional>
#include<algorithm>
#include<string>
#include<cmath>
#include<complex>
#include<set>
#include<map>
#include<stack>
#include<queue>
#include<tuple>
#define FOR(i,a,b) for(int i=(a);i<(b);i++)
#define REP(i,n) for(int i=0;i<(n);i++)
#define INF (int)1e9
#define INFL (ll)1e11
using namespace std;
typedef long long ll;

typedef pair<int, int> P;

void dfs(int s, int id, vector<vector<int>> a, vector<int> &comp) {
	stack<int> st;
	st.push(s);
	comp[s] = id;
	while (!st.empty()) {
		int i = st.top();
		int k = a[i].size();
		REP(j, k + 1) {
			if (j < k) {
				int t = a[i][j];
				if (comp[t] != id) {
					comp[t] = id;
					st.push(t);
					break;
				}
			}
			else st.pop();
		}
	}
}

void divide(int size, vector<vector<int>> a, vector<int> &comp) {
	int s = 0;
	int id = 1;
	while (1) {
		dfs(s, id, a, comp);
		while (s < size && comp[s]>0) s++;
		if (s == size) break;
		id++;
	}
	return;
}

int main() {
	//cin.tie(0);
	//ios::sync_with_stdio(false);

	int n, m;
	scanf("%d %d", &n, &m);
	//cin >> n >> m;
	vector<vector<int>> a(n);
	REP(i, m) {
		int s, t;
		scanf("%d %d", &s, &t);
		//cin >> s >> t;
		a[s].push_back(t);
		a[t].push_back(s);
	}
	int q;
	cin >> q;
	vector<int> comp(n, 0);
	divide(n, a, comp);
	REP(i, q) {
		int s, t;
		scanf("%d %d", &s, &t);
		//cin >> s >> t;
		if (comp[s] == comp[t]) printf("yes\n");
		else printf("no\n");
	}

	return 0;
}